Genotypic diversity and gene flow in brooding and spawning corals along the Great Barrier Reef, Australia

Marine organisms exhibit great variation in reproductive modes, larval types, and other life-history traits that may have major evolutionary consequences. We measured local and regional patterns of genetic variation in corals along Australia's Great Barrier Reef to determine the relative contributions of sexual and asexual reproduction to recruitment and to infer levels of gene flow both locally (among adjacent sites, < 5 km apart) and regionally (among reefs separated by 500-1,200 km). We selected five common brooding species (Acropora cuneata, A. palifera, Pocillopora damicornis, Seriatopora hystrix, and Stylophora pistillata) and four broadcast spawners (Acropora hyacinthus, A. cytherea, A. millepora, and A. valida), which encompassed a wide range of larval types and potential dispersal capabilities. We found substantial genotypic diversity at local scales in six of the nine species (four brooders, two spawners). For these six, each local population displayed approximately the levels of multilocus genotypic diversity (Go) expected for outcrossed sexual reproduction (mean values of Go:Ge ranged from 0.85 to 1.02), although consistent single-locus heterozygous deficits indicate that inbreeding occurs at the scale of whole reefs. The remaining three species, the brooder S. hystrix and the spawners A. valida and A. millepora displayed significantly less multilocus genotypic diversity (Go) than was expected for outcrossed sexual reproduction (Ge) within each of several sites. Acropora valida and A. millepora showed evidence of extensive localized asexual replication: (1) a small number of multilocus (clonal) genotypes were numerically dominant within some sites (Go:Ge values were as low as 0.17 and 0.20): (2) single-locus genotype frequencies were characterized by both excesses and deficits of heterozygotes (cf. Hardy-Weinberg expectations), and (3) significant linkage disequilibria occurred. For the brooding S. hystrix Go:Ge values were also low within each of four sites (x = 0.48). However, this result most likely reflects the highly restricted dispersal of gametes or larvae, because levels of genetic variation among sites within reefs were extremely high (FSR = 0.28). For all species, we detected considerable genetic subdivision among sites within each reef (high FSR-values), and we infer that larval dispersal is surprisingly limited (i.e., Nem among sites ranging from 0.6 to 3.3 migrants per generation), even in species that have relatively long planktonic durations. Nevertheless, our estimates of allelic variation among reefs (FRT) also imply that for all four broadcast spawning species and three of the brooders, larval dispersal is sufficient to maintain moderate to high levels of gene flow along the entire Great Barrier Reef (i.e., Nem among reefs ranged from 5 to 31). In contrast, widespread populations of S. hystrix and S. pistilata (the two remaining brooders) are relatively weakly connected (Nem among reefs was 1.4 and 2.5, respectively). We conclude that most recruitment by corals is very local, particularly in brooders, but that enough propagules are widely dispersed to ensure that both broadcast spawning and brooding species form vast effectively panmictic populations on the Great Barrier Reef.     

A molecular phylogenetic analysis of reproductive trait evolution in the soft coral genus Alcyonium

The soft coral genus Alcyonium is among the most reproductively diverse invertebrate taxa known: The genus includes species that vary both in mode of reproduction (including broadcast spawners, internal brooders, and external brooders) and sexual expression (gonochores, hermaphrodites, and a unisexual parthenogen). Such diversity offers a unique opportunity to examine associations between reproductive and morphological traits in a phylogenetic context. We used an approximately 900-bp sequence of the nuclear ribosomal gene complex spanning the internal transcribed spacer (ITS) regions to construct a molecular phylogeny for 14 European and North American species of Alcyonium onto which we mapped the known distribution of reproductive and morphological traits. The phylogeny suggests that hermaphroditism or parthenogenesis has evolved independently at least twice in this genus, and always in internally brooding species. Broadcast spawning and external brooding only occur in species with large colony size, whereas all species with small colony size brood their larvae internally. Internal brooding and small size appear to be ancestral in this genus; if this is the case, an association between broadcast spawning and large colony size has evolved independently in at least two clades. This tendency of small adults to brood their larvae while large adults broadcast spawn them into the plankton has been observed in a variety of solitary invertebrate taxa, but to date has not been documented in any other colonial invertebrates. Moreoever, it has been suggested that organisms with a colonial growth form should not experience the allometric constraints on brood space that have been proposed to explain the association between adult size and mode of reproduction in solitary organisms. Unlike many other colonial groups, however, module (polyp) size is strongly correlated with colony size in Alcyonium, and constraints on brooding may be imposed by module, rather than colony, allometry. The very close genetic relationship (< 1% sequence divergence) and shared polymorphisms among A. digitatum (a large, gonochoric broadcast spawner), A. siderium, and A. sp. A (intermediate-sized and small hermaphroditic, internal brooders) suggest that evolutionary transitions between broadcast spawning and brooding and between gonochorism and hermaphroditism can occur easily and rapidly in this group.     

Correlated evolution of sex and reproductive mode in corals (Anthozoa: Scleractinia)

Sexuality and reproductive mode are two fundamental life-history traits that exhibit largely unexplained macroevolutionary patterns among the major groups of multicellular organisms. For example, the cnidarian class Anthozoa (corals and anemones) is mainly comprised of gonochoric (separate sex) brooders or spawners, while one order, Scleractinia (skeleton-forming corals), appears to be mostly hermaphroditic spawners. Here, using the most complete phylogeny of scleractinians, we reconstruct how evolutionary transitions between sexual systems (gonochorism versus hermaphrodism) and reproductive modes (brooding versus spawning) have generated large-scale taxonomic patterns in these characters. Hermaphrodites have independently evolved in three large, distantly related lineages consisting of mostly reef-building species. Reproductive mode in corals has evolved at twice the rate of sexuality, while the evolution of sexuality has been heavily biased: gonochorism is over 100 times more likely to be lost than gained, and can only be acquired by brooders. This circuitous evolutionary pathway accounts for the prevalence of hermaphroditic spawners among reef-forming scleractinians, despite their ancient gonochoric heritage.     

Gametic, morphometric, and physiological variables influencing clutch size in the Chilean oyster, Ostrea chilensis (Philippi, 1845)

A number of marine bivalve taxa, including species of the genus Ostrea, have adopted brooding of the young in the mantle cavity as a reproductive mechanism. In spite of the importance of brooding in the reproductive success of such species, little is known about the most important variables influencing the process, including those limiting clutch size. This study addresses the regulation of brood size in the hermaphroditic oyster Ostrea chilensis. During spawning, oysters released all their oocytes into the mantle cavity. No residual oocytes remained in the gonad, so a second spawning during the same brooding season was not possible. There was a weak correlation between the number of embryos incubated during the early phase of brooding and the dry tissue weight of the brooding oyster, and between the number incubated and the shell length of the brooding adult during the later phases of brooding. The number of embryos was also correlated with the area of the labial palps of the brooder during the later stages, suggesting that the loss of veligers observed at this time may be at least partially attributable to a limitation of space around the palps, which manipulate the larvae and with which the larvae are closely associated. The oxygen consumption rate of brooders incubating a normal clutch of embryos was not significantly different from that of oysters in which clutch size had been experimentally reduced by 50%. Experimental increase of the normal clutch size by 100% significantly increased the oxygen consumption of the brooder, suggesting that there is a physiological as well as a spatial limit to brood size. Thus the number of embryos brooded by an oyster is initially dependent on its production of oocytes and secondarily by the high metabolic costs of incubating large numbers of embryos. As development proceeds, space available for brooding apparently becomes a limiting factor as the larvae grow. The fate of the excess larvae is not known at present, but any larvae released prematurely cannot be competent to settle, since development is synchronous and there is a complete release of all pediveligers at the end of the brooding period.     

Studies on effective PCR screening strategies for white spot syndrome virus (WSSV) detection in Penaeus monodon brooders.

We re-tested stored (frozen) DNA samples in 5 independent polymerase chain reaction (PCR) replicates and confirmed that equivocal test results from a previous study on white spot syndrome virus (WSSV) in brooders and their offspring arose because amounts of WSSV DNA in the test samples were near the sensitivity limits of the detection method. Since spawning stress may trigger WSSV replication, we also captured a fresh batch of 45 brooders for WSSV PCR testing before and after spawning. Replicates of their spawned egg batches were also WSSV PCR tested. For these 45 brooders, WSSV prevalence before spawning was 67% (15/45 1-step PCR positive, 15/45 2-step PCR positive and 15/45 2-step PCR negative). Only 27 (60%) spawned successfully. Of the successful spawners, 56% were WSSV PCR positive before spawning and 74% after. Brooders (15) that were heavily infected (i.e. 1-step PCR positive) when captured mostly died within 1 to 4 d, but 3 (20%) did manage to spawn. All their egg batch sub-samples were 1-step PCR positive and many failed to hatch. The remaining 30 shrimp were divided into a lightly infected group (21) and a 2-step PCR negative group (9) based on replicate PCR tests. The spawning rates for these 2 groups were high (81 and 78%, respectively). None of the negative spawners (7) became WSSV positive after spawning and none gave egg samples positive for WSSV. In the lightly infected group (21), 6 brooders were 2-step WSSV PCR negative and 15 were 2-step WSSV PCR positive upon capture. However, all of them were WSSV PCR positive in replicate tests and after spawning or death. Four died without spawning. The remaining 17 spawned but only 2 gave egg samples PCR negative for WSSV. The other 15 gave PCR positive egg samples, but they could be divided into 2 spawner groups: those (7) that became heavily infected (i.e. 1-step PCR positive) after spawning and those (8) that remained lightly infected (i.e. became or remained 2-step PCR positive only). Of the brooders that became heavily infected after spawning, almost all egg sample replicates (91 %) tested 2-step PCR positive. One brooder even gave heavily infected (i.e. 1-step PCR positive) egg samples. For the brooders that remained lightly infected after spawning, only 27% of the egg sample replicates were 2-step PCR positive. Based on these results, we recommend that to avoid false negatives in WSSV PCR brooder tests screening tests should be delayed until after spawning. We also recommend, with our PCR detection system, discarding all egg batches from brooders that are 1-step PCR positive after spawning. On the other hand, it may be possible with appropriate monitoring to use eggs from 2-step PCR positive brooders for production of WSSV-free or lightly infected postlarvae. These may be used to stock shrimp ponds under low-stress rearing conditions.     

Comparison of testes structure,spermatogenesis, and spermatocytogenesis in young,aging, and hybrid cichlid fish (Cichlidae,Teleostei)

Testis structure, spermatogenesis, and spermatocytogenesis were compared in 13 species of cichlid fishes, belonging to the subfamilies Haplochrominae and Tilapinae. The species studied were either mouth brooders, in which fertilization occurs mostly inside the mouth of the brooding fish, or substrate brooders, whose eggs adhere to a substrate over which the sperm is ejaculated. In this study, the embryogenesis of testes anlagen and sperm production was followed in embryos and in fish up to 15 years old, as well as in hybrids of the two subfamilies. In cichlids, the testes are of the unrestricted type and primary spermatogonia develop along the entire length of the developing sperm tubule. The first primary spermatogonia are observed in the testes anlagen 2-5 days after fertilization and they continue to develop in cysts formed by the enveloping Sertoli cells and the intertubular elements. The dimensions of such primary and secondary spermatocysts are correlated with the number of spermatogonia they contain and the corresponding number of mitotic multiplications. The largest mature cysts attained 300 microm, and contained 2,200-2,400 spermatids in the mouth-brooding species and 2,600-3,200 in the substrate-brooding species. Despite the fact that in such cysts cytoplasmic bridges connect only the isogamete spermatids, the maturation of all cells and consequent spermiation is synchronized. Meristic characters distinguish the sperm of mouth brooders from those of substrate brooders, especially in the number of mitochondria and length of the flagellum. In older fish and hybrids, various changes can be seen in the gametogenic epithelium and intertubular cells. These include thickening of the connective tissue, formation of "yellow" groups of Leydig cells, cell apoptosis and degeneration, and, especially, formation of large spermatogonia, with large, electron-dense nucleoli, that have the cytological characteristics of oocytes. The intra- and interspecific variability of sperm dimensions in the studied cichlids poses an interesting question in the context of sperm competition.     

Contributions of growth, stasis, and reproduction to fitness in brooding and broadcast spawning marine bivalves

Reproductive modes in marine invertebrates can be generally grouped into two types: those brooding larvae and those broadcast-spawning gametes into the water. We asked if these different life-history strategies differ based on how contribution to fitness is partitioned between growth, stasis, and reproduction. To investigate this question, we used published demographic data on ten diverse species of marine bivalves. We parameterized simple matrix-population models and calculated the sums of elasticities to growth, stasis, and reproduction parameters and plotted the results on triangular axes. We also assessed whether contribution patterns were correlated with reproductive mode and tropical, temperate, or polar environments. We found that some of the broadcast spawners fell in the region of the plot with high elasticities for stasis and that some of the brooders fell in the region of the plot with higher growth and reproduction elasticities than stasis ones. However, instead of a sharp dichotomy, we found a continuum in contributions of stasis parameters with long-lived brooders and short-lived broadcast spawners in the same region of the plot. There was no clear pattern of reproductive mode associated with any particular environment, but we think these preliminary results are intriguing and that further work on comparative demography of marine invertebrates is warranted. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Diverse parentage relationships in paternal mouthbrooding fishes

While mouthbrooding is not an uncommon parental care strategy in fishes, paternal mouthbrooding only occurs in eight fish families and is little studied. The high cost of paternal mouthbrooding to the male implies a low risk of investment in another male''s offspring but genetic parentage patterns are poorly known for paternal mouthbrooders. Here, we used single-nucleotide polymorphism genetic data to investigate parentage relationships of broods of two mouthbrooders of northern Australian rivers, mouth almighty Glossamia aprion and blue catfish Neoarius graeffei. For N. graeffei, we found that the parentage pattern was largely monogamous with the brooder male as the sire. For G. aprion, the parentage pattern was more heterogeneous including observations of monogamous broods with the brooder male as the sire (73%), polygyny (13%), cuckoldry (6%) and a brood genetically unrelated to the brooder male (6%). Findings demonstrate the potential for complex interrelationships of male care, paternity confidence and mating behaviour in mouthbrooding fishes.     

An induced mass spawn of the hermaphroditic lion-paw scallop, Nodipecten subnodosus: genetic assignment of maternal and paternal parentage

The Pacific lion-paw scallop is commonly propagated for aquaculture by induced mass spawns of few individuals. Parentage of a mass spawn of this species has not been evaluated nor has the maternal and paternal contribution of each of these functional hermaphrodites to the progeny. Genotypes of 6 spawners and 374 resulting progeny at 6 microsatellite loci were coupled with mitochondrial DNA sequencing to assign maternal and paternal parentage. After the identification of a high proportion of null alleles (9.7%), microsatellite data revealed that 51.7% of the progenies were full siblings, with a significant, unequal contribution of the 6 spawners to the progeny. Three progenies were the result of self-fertilization. All spawners contributed paternally (though unequally); however, 2 spawners were the maternal parents of all but 7 progenies resulting in a variance effective population size of 3.52. DNA sequencing confirmed 4 microsatellite mutations within 4476 alleles scored, all in the paternal germ line. With minor exception, the loci conformed to Mendelian rules of segregation when null alleles were accounted for, and 2 loci were found to be linked. These results lend insight to the genetic composition of induced mass spawns and provide a basis for the development of more effective spawning techniques.     

Broadcasting fables: Is external fertilization really primitive? Sex,size, and larvae in sabellid polychaetes

Traditionally, broadcast spawning and planktonic larvae have been considered the plesiomorphic ‘ground plan’ for the Polychaeta and other metazoan groups. To assess whether this reproductive mode is in fact ‘primitive’, the study of monophyletic groups with various reproductive modes should be informative. A large range of body sizes would allow testing the ideas that aspects of reproductive mode may be functionally constrained. The family Sabellidac is one such group, with sexual reproductive modes ranging from broadcast spawning to intratubular brooding to ovovivi-parity, and a body size range over more than five orders of magnitude. Sabellids have previously been the subject of detailed cladistic analyses (Fitzhugh 1989, 1991); here we introduce several new characters based on morphology of reproductive structures. Larval development in four brooding sabellid species is also described with the aim of introducing new characters for future systematic analyses. Our cladistic analysis of sabellid genera suggests that gonochorism and brooding of direct-developing larvae are plesiomorphic in the Sabellidae, with external fertilization and swimming larvae limited to apomorphie clades in the subfamily Sabellinae. The presence of sperm with elongate heads may be correlated with the presence of intratubular brooding, though an adequate causal explanation for this relationship can not yet be presented. The concept that ‘modified’ sperm must be derived from ‘primitive’ sperm is shown to be false, with ‘modified’ sperm being plesiomorphic for the Sabellidae, from which ‘primitive’ sperm is derived in apomorphic Sabellinae. All sabellids have lecithotrophic development and appear to be phylogenetically constrained in this regard. Data gathered on body size and reproductive variables in the Sabellidac suggests the following (when phylogenetic effects are not controlled): (1) egg number and total egg volume are significantly correlated with body size, with small animals having fewer, larger eggs than large animals; (2) individual egg volume is not correlated with body size; (3) reproductive mode is significantly correlated with body size; intratubular brooders tend to be small-bodied, whereas broadcast spawners are large. However when the effect of body size is controlled for, then (4) egg number, egg volume and total egg volume all vary significantly with reproductive mode. Broadcast spawners expel a large number of small eggs for a high total egg volurne. Intratubular brooders have a few relatively large eggs for a small total egg volume. When statistics arc performed using phylogenetically independent contrasts there is a significant correlation between total egg volume and body size but not for egg number and body size. The effect of non-independence (due to phylogeny) of our data needs to be more fully controlled in future analyses but methods of incorporating continuous data into cladistic analyses should also be investigated. We show that some predictions can be made about reproductive mode based on body size but ad hoc patterns of reproductive character-state transformation should not be made independent of empirical hypotheses of phylogenetic relationship. Further studies of this kind throughout the Annelida are needed to determine the plesiomorphic reproductive mode for the phylum.     

Genetic data,reproduction season and reproductive strategy data support the existence of biological species in Ophioderma longicauda

Cryptic species are numerous in the marine environment. The brittle star Ophioderma longicauda is composed of six mitochondrial lineages, encompassing brooders, which form a monophyletic group, and broadcasters, from which the brooders are derived. To clarify the species limits within O. longicauda, we compared the reproductive status of the sympatric lineages L1 and L3 (defined after sequencing a portion of the mitochondrial gene COI) during the month of May in Greece. In addition, we genotyped a nuclear marker, intron i51. Each L3 female was brooding, whereas all L1 specimens displayed full gonads, suggesting temporal pre-zygotic isolation between brooders and broadcasters. Statistical differences were found among lineages in morphology and bathymetric distribution. Finally, the intron i51 was polymorphic in L1 (60 individuals), but monomorphic in L3 (109 individuals), confirming the absence of gene flow between brooders and broadcasters. In conclusion, the broadcasting lineage L1 and the brooding lineage L3 are different biological species.     

The influence of season and the tidal cycle on division of labour by the radula during feeding in the estuarine brooding gastropod <Emphasis Type="Italic">Crepipatella dilatata</Emphasis> (Calyptraeidae)

The brooding gastropod Crepipatella dilatata can feed by scraping the substrate with the radula and by suspension-feeding, which also requires use of the radula. There is a “division of labour” for the radula among three discrete tasks associated with feeding: (1) removing mucous balls from the food pouch; (2) transferring the mucous cord from the neck channel to the mouth (both components of suspension-feeding); (3) scraping the substrate. We hypothesised that the proportion of time used for each feeding activity varies according to environmental conditions. Total radular activity in females was greatest at high tide and in summer. The rate of radular extrusion for ingesting the mucous cord varied seasonally and between brooding and non-brooding females. Non-brooding females exhibited higher rates of radular extrusion for ingesting the mucous cord and for scraping the substrate than did brooders. In females, radular activity in removing the mucous ball from the food pouch was strongly influenced by the tidal cycle during winter, reaching minimum values at low tide. Differences were recorded in substrate scraping among seasons and within tidal cycles, and among males, brooding females and non-brooding females. Brooding females displayed less rasping than non-brooders, since the area available for grazing was restricted by the egg mass. Throughout the year, including low salinity periods, males allocated a greater proportion of total radular activity to rasping than to removing the mucous ball or ingesting the mucous cord. The feeding behaviour of both males and females is modulated by salinity, but the principal determinants of radular activity are the mode of reproduction (brooding in females) and, in males, motility.     

The evolution of mating systems in a group of brooding sea anemones (Epiactis)

Summary

The sea anemone genus Epiactis provides an unusually good opportunity to study the evolution of brooding and mating systems. The four Epiactis species on the Pacific coast of North America all brood their offspring up to the juvenile stage, but each has a different combination of internal vs. external brooding and gonochory vs. simultaneous or gynodioecious hermaphroditism. Two of the four species (E. prolifera and E. lisbethae) were indistinguishable with allozymes (20 loci), but could be differentiated using multilocus DNA fingerprinting. Phylogenetic analyses of the allozyme data by distance and parsimony methods using three outgroups suggest that the four nominal Epiactis species are polyphyletic, with the two internal brooders evolving independently of the two external brooders. This topology does not allow inferences about the evolutionary order of hermaphroditism, dioecy and gynodioecy. Separate sexes and obligate outcrossing are of ten believed to be ancestral, with hermaphroditism and the potential for self-fertilization being favored in taxa where restricted dispersal promotes inbreeding. Previous studies of population genetic structure in these Epiactis species is consistent with this hypothesis, as even the cross-fertile species were highly inbred.     

Experimental taphonomy of embryo preservation in a Cenozoic brooding bivalve

To distinguish between alternative explanations for the presence of synchronous broods in the Miocene-Pliocene bivalve, Transenriella species. we performed in situ burial experiments of the Recent species T. corfusa . All Recent Transennella species are asynchronous brooders; a single brood contains all or most developmental stages. Specimens from Miocene—Pliocene deposits of California suggest that some members of this taxon were synchronous brooders, i.e., all the embryos of a brood develop simultaneously with only one developmental stage represented at any time. The presence of synchronous Transennella broods in the Miocene—Pliocene could indicate that an evolutionary change in mode of reproduction has occurred in this genus. Alternatively, asynchronous brooding in this taxon may he conservative and preferential preservation of later stages of development, or seasonal variation in reproduction, could result in a taphonomic overprint. Our burial experiments indicate that the earliest stages of development are almost entirely lost; however. there is enough preservation of the later stages of development to distinguish the two modes of reproduction. Additionally. we discovered a single fossil specimen with an asynchronous brood. Based primarily on this specimen, and observations from the burial experiments, we conclude that the fossil synchronous broods are an artifact of preservation and asynchronous brooding in Transenella is conservative.     

Reproductive ecology of Caribbean reef corals

The last decade has seen a resurgence of interest in the processes of sexual reproduction by scleractinian reef corals. Earlier investigations had focused fortuitously on brooding (planulating) species, which resulted in the general misconception that brooding was the main form of larval development of reef corals. More recent work on Indo-Pacific species has shown broadcast spawning and short annual reproductive periods to predominate. This report presents the reproductive patterns of eleven Caribbean coral species and attempts to explain the adaptive features and selective pressures that have led to the evolution of the four reproductive patterns described to date: (a) hermaphroditic broadcasters; (b) gonochoric broadcasters; (c) hermaphroditic broadcasters; (b) gonochoric brooders. Both (a) and (b) correlate with large colony size and short annual spawning periods; and (c) and (d) correlate with small colony size, multiple planulating cycles per year, and occupation of unstable habitats. Selection for outcrossing between long-lived individuals is proposed as the reason for gonochorism and for synchronous spawning of hermaphroditic broadcasters, and also for the large amount of sperm produced by hermaphroditic brooders. Selection for high rates of local recruitment is proposed as the force behind the evolution of brooding by species inhabiting unstable habitats and suffering high rates of adult mortality.     

Sexual reproduction in Epistomia bursaria (Bryozoa: Cheilostomata), an endozooidal brooder without polypide recycling

Epistomia bursaria L. is unusual amongst cheilostomes in that there is only one polypide generation per autozooid, together with endocoelomic embryonic brooding and larval viviparity. This combination, which gives the minimum possible fecundity of one larva per gynozooid is only known for one other cheilostome species, the majority of the rest being extracoelomic ovicellate brooders with polypide recycling. The greater fecundities exhibited by ovicellate and non-brooding recyclers may offset the smaller degree of protection afforded by these reproductive strategies.
Spermatogenesis and oogenesis are examined ultrastructurally. Whereas spermatogenesis is similar to that of other cheilostomes studied previously, oogenesis is very different. The egg at maturity is small and alecithal. Evidence suggests that endozooidal self-fertilization occurs. Whereas nutrient for spermatogenesis and oogenesis is probably intrazooidal in origin, that for embryogenesis is derived inter-zooidally.
It is suggested that the combination of endocoelomic brooding, larval viviparity and one polypide generation may be a primitive feature from which recycling and extracoelomic brooding may have evolved.     

Diet-morphology correlations in the radiation of South American geophagine cichlids (Perciformes: Cichlidae: Cichlinae)

Genera within the South American cichlid tribe Geophagini display specialized feeding and reproductive strategies, with some taxa specialized for both substrate-sifting and mouth brooding. Several lineages within the clade also possess an epibranchial lobe (EBL), a unique pharyngeal structure that has been proposed to have a function in feeding and/or mouth brooding. A recently published genus-level phylogeny of Neotropical cichlids was used as the evolutionary framework for investigating the evolution of morphological features presumably correlated with diet and mouth brooding in the tribe Geophagini. We tested for possible associations between the geophagine epibranchial lobe and benthic feeding and mouth brooding. We also addressed whether the EBL may be associated with unique patterns of diversification in certain geophagine clades. Tests of binary character correlations revealed the EBL was significantly associated with mouth brooding. We also tested for a relationship between diet and morphology. We analyzed stomach contents and morphometric variation among 21 species, with data for two additional species obtained from the literature. Principal Components Analysis revealed axes of morphological variation significantly correlated with piscivory and benthivory, and both morphology and diet were significantly associated with phylogeny. These results suggest that the EBL could be an adaptation for either feeding or mouth brooding. The EBL, however, was not associated with species richness or accelerated rates of phyletic diversification.     

Patterns of Parental Investment and Sexual Selection in Teleost Fishes: Do They Support Bateman's Principles?

Bateman demonstrated differences in variance for fertility andmating success between the sexes, with males usually havinga greater variance than females. Thus in general, male reproductivesuccess increases with number of mates acquired. These resultshave been referred to as "Bateman's principles" and taken togetherwith other parameters (e.g., relative parental investment) havebeen proposed to estimate a component of sexual selection. Forthis review I examine patterns of parental care and sexual selectionin teleost fishes (substrate brooding and with internal fertilization).I present data for the pumpkinseed sunfish Lepomis gibbosus,in which I estimated cost of paternal care and compared directmeasures of the intensity of selection on possible sexuallyselected traits to measures of sexual selection based on Bateman'sprinciples. Despite high levels of paternal care in substrate brooding fishes,sexual selection tends to act more strongly on males than onfemales, which suggests that maternal investment is higher thanpaternal investment and that parental care does not limit thereproductive rate for males. In pumpkinseed sunfish, selectionfavors parents with high levels of defense that may excludepredators more effectively and, as suggested by Bateman's measures,alternative reproductive strategies may decrease the opportunityfor sexual selection within the parental strategy. In teleostfishes with internal fertilization, patterns of parental investmentand intensity of sexual selection seem to support Bateman'sprinciples, but further studies using these systems and thesemeasures of selection will improve the understanding of factorsaffecting the intensity of sexual selection and its relationto mating systems.     

Early release of eggs and embryos in a brooding ancient asexual ostracod: brood selection or a gambling strategy to increase fecundity?

Asexual lineages lack the means to purge their genomes of (deleterious) mutations through recombination. Evolutionary theory thus predicts that such lineages will be prone to early extinction. In brooding animals, brood selection might provide a mechanism to counter the accumulation of mutations. Of the three putative ancient asexual animal groups, only the darwinulid ostracods are brooders. Here, we test the incidence of egg and juvenile abortion in a darwinulid species, Penthesilenula brasiliensis, under two temperature treatments. Part of the offspring is released without brooding (close to 30% in one treatment). The majority of these aborted eggs hatches and develops. As it is unlikely that females are such bad judges of offspring quality, either the surviving animals will present deficiencies later on in development (brood selection) or early egg release can be a (bet-hedging) strategy to increase fecundity in favourable conditions.     

Hermaphroditism in molluscs

The functional significance of hermaphroditism is, as yet, not well understood. This study attempts to examine the relevance of some theories on this topic to reality, by reviewing the literature on hermaphroditism among molluscs. The study reveals that about 40% of the 5600 mollusc genera are either simultaneous or sequential hermaphrodites. Hermaphroditism occurs in 100% of the Solenogastres, 99% of the Opisthobranchia, 100% of the Pulmonata, 3% of the Prosobranchia and 9% of the Bivalvia. Sequential hermaphroditism, whatever its theoretical advantages over gonochorism, is not common among molluscs. Simultaneous hermaphroditism is common among the Euthyneura. Over 80% of the hermaphroditic genera belong to the Euthyneura (about 2000 recent genera), and over 99% of the Euthyneura are hermaphrodites. The almost ubiquitous occurrence of hermaphroditism throughout the Euthyneurans, coupled with this group's very widespread dispersal in marine, terrestrial and freshwater habitats (and corresponding exposure to a very wide range of predators, competitors or parasites); and also its wide range of population densities, suggests that in this group hermaphroditism is not an adaptive response to selective forces of the environment and it may well be a phylogenetic constraint. A few stylommatophorans have broken this constraint by possessing genitalia in which the male system is absent (aphally) or extremely reduced (hemiphally). They reproduce by self-fertilization. In theory this is advantageous in that these species save the cost of developing two sets of reproductive apparatus. In reality there is no record of aphally occurring throughout an entire species, as one may expect if this saving of cost were so overwhelmingly advantageous. There is also no record of stylommatophoran individuals developing only the male system, as one may expect if there was any evolutionary trend from hermaphroditism towards gonochorism. Simultaneous hermaphroditism offers a (theoretical) option to selling. Selfing by self-fertilization is widespread among freshwater basommatophorans, amphibious stylommatophorans and freshwater bivalves. Selfing by parthenogenesis is widespread among freshwater prosobranchs. Altogether, of 48 genera which self, 60% are dwellers of freshwater. Certain freshwater habitats may perhaps be less stable than most marine or terrestrial ones are. Beyond the Euthyneura, hermaphroditism is common among parasitic, deep sea and Cnidaria-eating molluscs. Perhaps these three associations should be slightly rearranged and combined into a single generalization: that hermaphroditism (beyond the Euthyneura) is widespread among molluscs that live in a close and permanent intimacy with live marine invertebrates, whether as parasites, commensals or predators. Gonochorism but with dwarf males is common among the Eulimoidea, which are parasites, and Galeommatoidea, which are commensals. This situation of gonochorism, in which there is a very close association between members of the two sexes, is functionally a hermaphroditic type. Animals that can manipulate the physiology and endocrinology of their hosts may also have the tendency and ability to manipulate the size of their own males. It may well be that the female not only determines the size of the male but also his sex, in which case dwarf males should be considered as a case of environmental sex determination. The theoretical possibility that hermaphroditism may evolve in brooding animals was examined in gastropods. Among the (predominantly gonochoric) prosobranchs brooding is recorded in 85 genera (4%), only two of which are hermaphrodites. Among the (predominantly hermaphrodite) heterobranchs it is recorded in only 95 odd genera (4%). When all gastropod genera are considered together, the frequency of hermaphroditism among the brooders is only very slightly and insignificantly higher than in the non-brooders. When only the prosobranchs are considered, the frequency of hermaphroditism among the brooders is actually lower than among non-brooders. The theory that hermaphroditism evolves in brooding animals thus appears not to be relevant to the vast majority of gastropods. Brooding is widespread among freshwater prosobranchs (48% of the brooding genera). In this habitat, brooding may perhaps be an adaptation to protect the developing embryo against osmotic stresses.