Female reproductive morphology of coral‐inhabiting gall crabs (Crustacea: Decapoda: Brachyura: Cryptochiridae)

Gall crabs are obligate associates of stony corals in which they induce skeletal modifications. In some cryptochirid species, females live in open depressions accessible to males; while in others, females are rather isolated in semiclosed galls, which necessitates elaborate sperm storage capabilities by the female. In this study we investigate the female gross morphology and reproductive systems of Fungicola syzygia lodged in semiclosed flattened pits, Opecarcinus cathyae with semiopen pits and Pseudocryptochirus viridis from shallow open depressions using line drawings and histological methods. The general morphology of the cryptochirids' reproductive systems is uniform and conforms to other thoracotreme brachyurans: paired muscular vaginae of the concave pattern lead from the sternal gonopores into paired seminal receptacles where sperm is stored. The seminal receptacle is internally lined by distinct types of epithelia: a cuticle underlined by a columnar epithelium ventrally, a monolayered secretory epithelium dorsally and a multilayered transfer tissue where the oviducts enter the seminal receptacle. In all studied specimens, the seminal receptacle contained free spermatozoa; however, in specimens of Pseudocryptochirus viridis it also contained spermatophores, indicating a recent insemination. In contrast to most other brachyurans ovaries of the investigated cryptochirids extend into the pleon. The specific degree of ovary extension differs between the studied species and is closely related to female body shape.     

Relationship of Homolidae and Dromiidae: Evidence from Spermatozoal Ultrastructure (Crustacea,Decapoda)

Abstract The homolid spermatozoon, as exemplified by Homolasp., Paromolasp. and Paromola petterdi, differs markedly from spermatozoa of crabs of the Heterotremata–Thoracotremata assemblage but agrees with the sperm of dromiids, in the strongly anteroposteriorly depressed acrosome (apomorphy?) and the capitate form of the perforatorium (a major synapomorphy seen nowhere else in the Crustacea). These similarities support inclusion of the Dromiidae and Homolidae in a single grouping, the Podotremata. The homolid perforatorium differs from that of dromiids in the autapomorphic spiked–wheel form of the anterior expansion. Homolid spermatozoa show nuclear arms symplesiomorphic of all investigated crabs (small or questionably sometimes absent in Dromiidae), and corresponding loss of purely microtubular arms seen in other reptants. Homolid sperm agree with those of dromiids (synapomorphy?), raninids, higher heterotremes and thoracotremes (homoplasies?) but differ from lower heterotremes, in lacking microtubules in the nuclear arms. A posterior median process of the nucleus in homolids, not seen in dromiids, is shared with anomurans and lower heterotremes. No features in the ultrastructure of homolid or dromiid sperm have been detected which associate them exclusively with either the Raninidae or the heterotreme and thoracotreme Brachyura.     

The reproductive system of Limnopilos naiyanetri indicates a thoracotreme affiliation of Hymenosomatidae (Decapoda,Eubrachyura)

The eubrachyuran Hymenosomatoidea is widely distributed in tropical and subtropical regions ranging from marine to freshwater habitats. Even though the biology of this taxon has been studied to some extent, its phylogenetic relationships are not resolved. Based on different morphological characters, some authors suggested a close affinity of hymenosomatid crabs to heterotremes. However, many of these characters are ambiguous, and the few molecular studies did not provide convincing solutions either. To address this issue, we studied the reproductive system of the hymenosomatid freshwater species Limnopilos naiyanetri Chuang and Ng, 1991 using histology and scanning electron microscopy. The females show the characteristic organization of the paired eubrachyuran reproductive system. Additionally, a bursa (an accessory sperm storing cuticle cavity) is present. The male copulatory system is characterized by paired long first and short second gonopods, and a pair of sternal gonopores equipped with a penis. Both, the female and male reproductive organs reveal a number of similarities to thoracotreme crabs. The seminal receptacle is lined by a very thin cuticle and by a mono-layered glandular epithelium. The male gonopods and the sternal genital opening also resemble the thoracotreme condition. Thus, our results indicate that Hymenosomatidae are most likely part of the Thoracotremata.     

Morphology of the female reproductive system of three dorippid crabs (Crustacea: Decapoda: Brachyura: Dorippidae) and the role of accessory cuticle structures associated with seminal receptacles

The reproductive systems of crabs reveal characters of considerable importance for the understanding of brachyuran phylogeny and evolution. The Dorippoidea show several plesiomorphic characters within Eubrachyura and similarities to podotreme crabs. Hence, they are often considered as an early diverging lineage, sometimes even as the sister group to all remaining eubrachyurans. Due to their role as prime candidates for putative plesiomorphic characters of the reproductive system of the Eubrachyura, we compared the morphology of the vaginae, seminal receptacles, and ovaries of three dorippid species using histological methods, micro‐computed tomography, and 3‐D reconstructions. Despite the putative phylogenetic position of dorippids, the female reproductive system shows features that are regarded as derived characters in eubrachyurans, including a concave vagina and a ventral‐type seminal receptacle. In contrast to other eubrachyurans, the oviduct does not enter the seminal receptacle directly but through specific cuticular valves. The female reproductive systems of Dorippe sinica and Dorippe quadridens are remarkable in further aspects. The seminal receptacles of both species are completely cuticle‐lined and have accessory sperm storage structures, the bursae. Our findings on the morphology of the female reproductive system of dorippids with its unique combination of basal, derived, and new characters challenges the prevailing hypothesis on the evolution of sperm storage organs in Eubrachyura.     

The male copulatory system of european pea crabs (crustacea,brachyura, pinnotheridae)

The male copulatory system of the European pinnotherid species Pinnotheres pisum, Pinnotheres pectunculi, and Nepinnotheres pinnotheres was investigated by gross morphology, scanning electron microscopy, histological methods, and confocal laser scanning microscopy. The brachyuran copulatory system is consistently formed by paired penes and two pairs of abdominal appendages, the gonopods, functioning in sperm transfer. In pinnotherids, the long first gonopods transfer the sperm mass into the female ducts. The first gonopod has the ejaculatory canal inside that opens both basally and distally. The second gonopod is solid, short, and conical. During copulation, the penis and the second gonopod are inserted into the basal lumen of the first gonopod. While the penis injects the sperm mass, the second gonopod functions in the transport of spermatozoa inside the ejaculatory canal toward its distal opening. The second gonopod is adapted for the sealing of the tubular system in the first gonopod by its specific shape and the ability to swell. Longitudinal cuticle foldings of the second gonopod hook into structures inside the first gonopod. The second gonopod can interact with the penis during copulation by a flexible flap separating the lumina in which the second gonopod and the penis are inserted. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Morphology and function of reproductive organs in Neodasys chaetonotoideus (Gastrotricha: Neodasys) with a phylogenetic assessment of the reproductive system in Gastrotricha

The reproductive system of the important basal gastrotrich Neodasys chaetonotoideus is described and reconstructed on the basis of light microscopy, serial ultrathin sections (ultrastructure) and scanning electron microscopy. Starting frontally, the hermaphroditic reproductive system consists of paired and tube shaped lateral testes that do not possess elongated seminal ducts but most likely open directly via paired ventral pores. The unpaired, medio‐dorsal ovary region contains early oogenic stages that mature caudally towards the uterus region, where the most mature egg is positioned laterally to the midgut. The ovary region is not covered with an epithelial lining whereas the uterus region possesses a distinct epithelial wall. Between ovary and uterus region, we have detected a conspicuous section of the female gonad, the vitellogenic oviduct that consists of a thick epithelial wall which forms cellular protuberances into the developing oocytes passing the oviduct. We interpret this as a special, hitherto undescribed mode of vitellogenesis in Gastrotricha. Further caudally, the uterus continues with the fronto‐caudal organ, a complex of two substructures that are apparently homologous to the frontal organ and the caudal organ of many species of the Gastrotricha Macrodasyida. Neodasys chaetonotoideus obviously engages in spermatophore formation and transfer. In this study we develop a morpho‐functional scenario for the gonads and accessory organs in terms of spermatophore production, exchange and oviposition. We compare our newly obtained data with already published results on the reproductive organs of several species of Gastrotricha by means of a species‐character matrix and provide a computer aided evaluation by a parsimonious character optimization. A reconstruction of the reproductive system of the stem species of Gastrotricha on the basis of three recent phylogenetic analyses is presented. These reconstructions give support for a Neodasys‐like reproductive system in the ground pattern of Gastrotricha with slight morphological differences and direct transfer of spermatozoa rather than spermatophore transfer. The evolution of selected characters is traced thus revealing some incidents of convergent evolution as well as the evolutionary replacement of the ancestral frontal organ by the derived frontal sac in at least two separated lineages.     

Morphology and function of the copulatory system in freshwater crabs of the genus Potamon

To understand the reproductive processes of freshwater crabs of the genus Potamon, we examined the first and second gonopod and the gonoducts of the female by histological methods. The gonopods are highly modified compared to those of other brachyuran crabs. In particular, the second gonopod is unusually long and has a special morphology, ending in a long sclerotized tube. Suggestions for the function of both gonopods and their different parts are presented. Tubulation of the first and second gonopod is observed. Rosette glands, which are abundant in the subterminal joint of the first gonopod, are connected to the sperm channel by cuticular pores. In females, the chitinous parts of the inner vulva may prove to have a more constant morphology than the external flexible structures. J. Morphol. 239:157–166, 1999. © 1999 Wiley‐Liss, Inc.     

Male internal reproductive structures of european pea crabs (Crustacea,Decapoda, Brachyura,Pinnotheridae): Vas deferens morphology and spermatozoal ultrastructure

Pea crabs of the subfamily Pinnotherinae (Pinnotheridae) have a high investment in reproduction and an outstanding reproductive output, probably as an adaptation to the required increase in reproductive rate due to the pinnotherids small size and their parasitic, host‐dependant way of life. In the present study, we investigate the male internal reproductive structures and the ultrastructure of spermatozoa of Pinnotheres pisum and Nepinnotheres pinnotheres by histological methods and both scanning‐ and transmission electron microscopy. In the Brachyura, the male internal reproductive systems generally consist of paired testes and corresponding vasa deferentia where spermatozoa develop and mature. Spermatozoal ultrastructure of the investigated pinnotherids conforms to the thoracotreme type, however, N. pinnotheres has an accessory opercular ring and a periopercular rim, neither of which are present in spermatozoa of P. pisum. Spermatozoa are enclosed within spermatophores in the secretory proximal vas deferens. Two types of secretions were observed in P. pisum and N. pinnotheres: an electron dense substance secreted in the proximal vas deferens involved in spermatophore formation, and large electron‐luscent vesicles constituting the seminal plasma in the medial and distal vas deferens. The medial vas deferens is strongly widened compared to other brachyurans to purpose storing spermatophores embedded in seminal plasma. Tubular appendices, which produce and store large amounts of seminal plasma, arise from the distal region of the vas deferens. The appendices extend into the ventral cephalothorax and also in the first pleomere. The latter being an exceptional location for reproductive structures among male brachyurans. J. Morphol. 274:1312–1322, 2013. © 2013 Wiley Periodicals, Inc.     

Molecular species delimitation methods recover most song‐delimited cicada species in the European Cicadetta montana complex

Molecular species delimitation is increasingly being used to discover and illuminate species level diversity, and a number of methods have been developed. Here, we compare the ability of two molecular species delimitation methods to recover song‐delimited species in the Cicadetta montana cryptic species complex throughout Europe. Recent bioacoustics studies of male calling songs (premating reproductive barriers) have revealed cryptic species diversity in this complex. Maximum likelihood and Bayesian phylogenetic analyses were used to analyse the mitochondrial genes COI and COII and the nuclear genes EF1α and period for thirteen European Cicadetta species as well as the closely related monotypic genus Euboeana. Two molecular species delimitation methods, general mixed Yule‐coalescent (GMYC) and Bayesian phylogenetics and phylogeography, identified the majority of song‐delimited species and were largely congruent with each other. None of the molecular delimitation methods were able to fully recover a recent radiation of four Greek species.     

On the marine sister groups of the freshwater crabs (Crustacea: Decapoda: Brachyura)

Freshwater crab sister group relationships with marine eubrachyuran families were investigated. A morphology-based cladistic analysis was conducted on representatives of the freshwater crab families Deckeniidae, Gecarcinucidae, Parathelphusidae, Potamidae, Potamonautidae, Pseudothelphusidae, and Trichodactylidae using a disparate assemblage of marine heterotreme and thoracotreme brachyurans as possible sister groups. The monophyly of the freshwater crabs sensu lato is falsified. The family Trichodactylidae and the marine portunid subfamily Carcininae form basal groups within the superfamily Portunoidea. The monophyly of the Pseudothelphusidae and the Paleotropical freshwater crab families is supported, and this clade is the sister group of the Thoracotremata (Gecarcinidae, Grapsidae s.l., and Ocypodoidea). The origin, groundplan, and diversification of freshwater crabs are discussed in the context of previously published scenarios of their evolution.     

Strong intraspecific variation in genetic diversity and genetic differentiation in Daphnia magna: the effects of population turnover and population size

Theory predicts that genetic diversity and genetic differentiation may strongly vary among populations of the same species depending on population turnover and local population sizes. Yet, despite the importance of these predictions for evolutionary and conservation issues, empirical studies comparing high‐turnover and low‐turnover populations of the same species are scarce. In this study, we used Daphnia magna, a freshwater crustacean, as a model organism for such a comparison. In the southern/central part of its range, D. magna inhabits medium‐sized, stable ponds, whereas in the north, it occurs in small rock pools with strong population turnover. We found that these northern populations have a significantly lower genetic diversity and higher genetic differentiation compared to the southern/central populations. Total genetic diversity across populations was only about half and average within‐population diversity only about a third of that in southern/central populations. Moreover, an average southern population contains more genetic diversity than the whole metapopulation system in the north. We based our analyses both on silent sites and microsatellites. The similarity of our results despite the contrasting mutation rates of these markers suggests that the differences are caused by contemporary rather than by historical processes. Our findings show that variation in population turnover and population size may have a major impact on the genetic diversity and differentiation of populations, and hence may lead to differences in evolutionary processes like local adaptation, hybrid vigour and breeding system evolution in different parts of a species range.     

Notes on the position of the true freshwater crabs within the brachyrhynchan Eubrachyura (Crustacea: Decapoda: Brachyura)

Cladistic and phenetic relationships of 51 eubrachyuran crab genera, comprising 36 genera of marine crabs and 18 genera of true freshwater crabs from 7 families, were investigated using 121 parsimony-informative adult morphological characters. The data matrix was subjected to four different treatments: (1) a cladistic analysis with a combination of unordered and ordered characters, (2) a cladistic analysis with all characters unordered, (3) neighbour-joining, and (4) UPGMA phenetic analyses. The parsimony analysis conducted with a combination of ordered and unordered characters produced a set of hypotheses which supported monophyly of a Pseudothelphusidae+Potamoidea clade. Furthermore, exemplar genera of the Bythograeidae and Pinnotheridae formed an unresolved polytomy with the Pseudothelphusidae+Potamoidea group, the Thoracotremata. The trichodactylid freshwater crabs were positioned as the sister taxon of the basal portunoid Carcinus, but were unresolved relative to other portunoids and geryonids. Second, the parsimony analysis conducted with all characters unordered resulted in a [bythograeid, pseudothelphusid+potamoid, pinnotherid, thoracotreme] group with no hierarchical resolution, which in turn formed a polytomy with a goneplacid+portunoid clade and a polyphyletic Xanthoidea. And third, phenetic groupings of the eubrachyuran genera invariably placed the pseudothelphusids with the potamoids, and this clustered with a group containing the thoracotremes (either in whole or part). Support was thus found for morphological connections among the nontrichodactylid freshwater crabs, thoracotremes, bythograeids, and pinnotherids, and for the placement of the trichodactylids within the Portunoidea. These two latter findings (that used a range of genera from each family) are broadly congruent with a previous cladistic analysis of selected eubrachyuran familial groundpatterns that used a basal exemplar of each marine and freshwater crab family (Sternberg et al., 1999). However, it is clear that the large scale homoplasy identified here may nullify any reliable hypothesis of brachyrhynchan groupings at this stage.     

The evolution of the reproductive system of Urodasys (Gastrotricha: Macrodasyida)

Macrodasyidan gastrotrichs are hermaphrodites with complex reproductive organs that function in sperm transfer and receipt, but homology among the organs of members of different clades remains undetermined, as does a broader understanding of evolutionary trends in the reproductive biology of macrodasyidans. In this study, we investigate the evolution of reproduction in Urodasys, a clade of 15 macrodasyidan species that shows variability in reproductive mode (hermaphroditic and parthenogenetic) and sexual anatomy. We use partial 18S rDNA sequence data from 30 specimens representing five described species, sequence data from one undescribed species in GenBank, and sequence data from a potentially new species found at Capron Shoal, Florida, to gain insight into the phylogeny of the clade and clarify evolutionary trends in reproductive modality. Based on a total of 33 specimens of seven potential species, we found that members of Urodasys can be separated into three clades reflective of different reproductive modalities: Clade I, species with paired male and female gonads but without accessory sexual organs; Clade II, species with a single left testis, paired ova, and accessory organs including a sclerotic stylet; and Clade III, parthenogenetic species without testes or accessory organs. In addition, we find that the potentially new species from Florida can form spermatophores, a condition shared with another species in Clade I. Herein, we describe this novel spermatophore‐bearing species and discuss the significance of spermatophore formation in the genus.     

Evolution of sociality in spiders leads to depleted genomic diversity at both population and species levels

Across several animal taxa, the evolution of sociality involves a suite of characteristics, a “social syndrome,” that includes cooperative breeding, reproductive skew, primary female‐biased sex ratio, and the transition from outcrossing to inbreeding mating system, factors that are expected to reduce effective population size (Ne). This social syndrome may be favoured by short‐term benefits but come with long‐term costs, because the reduction in Ne amplifies loss of genetic diversity by genetic drift, ultimately restricting the potential of populations to respond to environmental change. To investigate the consequences of this social life form on genetic diversity, we used a comparative RAD‐sequencing approach to estimate genomewide diversity in spider species that differ in level of sociality, reproductive skew and mating system. We analysed multiple populations of three independent sister‐species pairs of social inbreeding and subsocial outcrossing Stegodyphus spiders, and a subsocial outgroup. Heterozygosity and within‐population diversity were sixfold to 10‐fold lower in social compared to subsocial species, and demographic modelling revealed a tenfold reduction in Ne of social populations. Species‐wide genetic diversity depends on population divergence and the viability of genetic lineages. Population genomic patterns were consistent with high lineage turnover, which homogenizes the genetic structure that builds up between inbreeding populations, ultimately depleting genetic diversity at the species level. Indeed, species‐wide genetic diversity of social species was 5–8 times lower than that of subsocial species. The repeated evolution of species with this social syndrome is associated with severe loss of genomewide diversity, likely to limit their evolutionary potential.     

Induced defences alter the strength and direction of natural selection on reproductive traits in common milkweed

Evolutionary biologists have long sought to understand the ecological processes that generate plant reproductive diversity. Recent evidence indicates that constitutive antiherbivore defences can alter natural selection on reproductive traits, but it is unclear whether induced defences will have the same effect and whether reduced foliar damage in defended plants is the cause of this pattern. In a factorial field experiment using common milkweed, Asclepias syriaca L., we induced plant defences using jasmonic acid (JA) and imposed foliar damage using scissors. We found that JA‐induced plants experienced selection for more inflorescences that were smaller in size (fewer flowers), whereas control plants only experienced a trend towards selection for larger inflorescences (more flowers); all effects were independent of foliar damage. Our results demonstrate that induced defences can alter both the strength and direction of selection on reproductive traits, and suggest that antiherbivore defences may promote the evolution of plant reproductive diversity.     

Cryptic diversity of Melanochlamys sea slugs (Gastropoda,Aglajidae) in the North Pacific

North Pacific specimens of Melanochlamys sea slugs were examined morphologically (including the male reproductive morphology, shell and external coloration) and were sequenced for three genes (mitochondrial COI and 16S and nuclear H3). Phylogenetic and species delimitation analyses were used to determine the evolutionary relationships and species diversity among the specimens examined. Both molecular and morphological data revealed an unexpected high level of cryptic diversity. At least four distinct species occur on the Northwestern Pacific. Melanochlamys ezoensis occurs in Russia and temperate and cold areas in Japan. Three additional undescribed species occur in Japan and/or South Korea. One of the undescribed species occurs both in South Korea and in Japan, but only in Tokyo Bay, suggesting that it could be non‐native in Japan. Two distinct species occur on the Northeastern Pacific coast; Melanochlamys diomedea is widespread from Southern California to Alaska, whereas M. ezoensis was found only in San Francisco Bay, suggesting a human‐mediated introduction. This is further supported by the absence of records of M. ezoensis in San Francisco prior to 2001. The species diversity of Melanochlamys in the Northwestern Pacific is much greater than in the Northeastern Pacific; it is hypothesized that differences in geographic and ocean current system complexity might account for different responses to glacial extinction and postglacial expansion.     

The biogeography of plant reproduction: potential determinants of species' range sizes

Aim A major biogeographical hypothesis, the ‘niche‐breadth’ hypothesis, explains species range sizes based on the extent of a species’ niche (e.g. diversity of habitats occupied; range of environmental conditions tolerated). An alternative hypothesis explains range sizes using metapopulation theory (e.g. colonization dynamics; dispersal ability). Both niche breadth and colonization ability may be related to plant species’ reproductive characteristics. We evaluate both hypotheses by examining the relationship of plant range size to mating system and genomic structure (ploidy status). Location Western North America. Methods Using a data set of 60 taxa in the genus Clarkia (Onagraceae), we use three analytical techniques to examine the effect of reproductive characteristics on range size. We conduct cross‐species analyses of present‐day taxa to examine both mating system and polyploidy in relation to range size. We also conduct a phylogenetically independent contrasts analysis (using caic software) on the relationship of mating system to range size in diploid species. Third, we compare closely related taxon pairs that differ in mating system as an alternative method to control for phylogeny. Results Polyploid species have significantly larger ranges compared with diploid species. When considering only diploid taxa, no significant relationship is found for mating system in both cross‐species and phylogenetically independent contrasts analyses. The diploid pairwise analysis, comparing only the range sizes of direct sister taxa with alternative mating systems, does show a relationship, with outcrossing species having larger ranges than self‐fertilizing species. Main conclusions We argue that genetic diversity, colonization ability, or a combination of both factors may influence plant species’ range sizes. The significant pairwise analysis suggests that both the independent contrast and the cross‐species analysis may be confounded by polytomies of species at the terminal nodes of the phylogeny, indicating the importance of comparing the results of multiple analytical techniques. We propose that the range sizes of self‐fertilizing species have a bimodal distribution, obscuring the effect of mating system on range size, and that a broader survey of plant taxa will resolve the two modes from that of the outcrossing species. Lastly, polyploid species appear to show significantly larger range sizes than diploid species, irrespective of mating system.     

Phylogenetic implications of sperm storage in Podotremata: Histology and 3D‐reconstructions of spermathecae and gonopores in female carrier crabs (Decapoda: Brachyura: Homoloidea)

Female reproductive systems are important characters for understanding the evolution of Brachyura and resolving its phylogenetic relationships. We herein investigate a podotreme brachyuran reproductive system comprehensively for the first time studying spermathecae and gonopores of Homoloidea with histological methods, micro‐computer tomography and scanning electron microscopy. Our results show that spermathecal apertures are species‐specific and their shape corresponds closely to that of male copulatory organs. Apertures were either enclosed by membranous cuticle areas or otherwise occluded preventing direct access into spermathecae. 3D‐reconstructions reveal that spermathecae differ between the species Paromola cuvieri and Homola barbata with regard to the involvement of sternite 7 and 8, respectively, in forming the sperm storage chamber. The cuticle epithelium that lines the spermathecal chamber is irregular and distinct from the remaining cylindrical cuticle epithelium. A first uniramous pleopod was present in all homoloids studied and always held in a position to cover spermathecal apertures. Specific pulvinated cuticle structures present on both sides of the first pleopod are herein interpreted as adhesive structures functioning in reproductive processes. The coxal gonopores were enclosed by a laterally arising muscular mobile operculum that resembles opercula described in eubrachyuran vaginae, which raises the question whether these two structures are homologous. Our results are compared with data available for other brachyuran groups and discussed in terms of phylogenetic relationships within the Brachyura and possible functions in insemination and fertilization in Podotremata. J. Morphol. 278:89–105, 2017. ©© 2016 Wiley Periodicals,Inc.