Insemination,intrafollicular fertilization and development of the fertilization plug during gestation in Heterandria formosa (Poeciliidae)

The viviparous teleost Heterandria formosa is a remarkable species for its reproductive characters including: (a) the smallest oocyte in viviparous fish species; (b) a high level of matrotrophy with a complex placenta; and (c) the highest level of superfetation. Superfetation involves (d) the continuous development of oocytes and fertilization at the same time with embryos in gestation. The sequential fertilization of oocytes requires (e) storage of spermatozoa in the ovary. Among these characteristics, fertilization is of fundamental interest, specifically the intrafollicular fertilization of poeciliids, species that do not present micropyle, and the consequent formation of the fertilization plug, a structure developed at the periphery of the follicle where the entrance of spermatozoa occurs. Both processes intrafollicular fertilization and formation of the fertilization plug have been rarely described. There is only one study illustrating, the fertilization plug of H. formosa with a drawing. In the context of reproductive aspects of H. formosa, the goal of this study is to describe the morphology of the ovary during insemination, intrafollicular fertilization and development of the fertilization plug. After insemination, spermatozoa enter the ovary and occupy folds of the lamella near follicles of all stages of oogenesis, the delle, where the germinal epithelium establishes contact with the follicular epithelium. The results of the present study provide evidence that both epithelia open at the distal end of the delle, this morphological change allow that the spermatozoa to make contact with the zona pellucida of the oocyte. After fertilization, the delle becomes blocked by proliferation of cells of the germinal epithelium, to form the fertilization plug that persists throughout gestation. Abundant reticular fibers and blood vessels are seen around the fertilization plug. Persistence of the fertilization plug suggests that it could be the site where the juvenile will gain entrance to the ovarian lumen during birth.     

VARIATION IN OFFSPRING SIZE WITH BIRTH ORDER IN PLACENTAL FISH: A ROLE FOR ASYMMETRIC SIBLING COMPETITION?

Asymmetric sibling competition arises when siblings with different competitive abilities share a limited resource. Such competition occurs in species with postnatal parental care and may also occur when mothers provision embryos between fertilization and birth (matrotrophy). We hypothesized that the combination of matrotrophy and the simultaneous provisioning of embryos in different stages of development (superfetation) leads to asymmetric competition between sibling embryos. Moreover, we expect the intensity of this competition to increase with the level of superfetation as high levels of superfetation result in greater temporal overlap between broods. This hypothesis predicts that offspring from early broods, which predominantly compete with less‐developed siblings, will be larger at birth than offspring from later broods, which experience competition from more and less‐developed siblings. Data on offspring size at birth from two populations of the highly matrotrophic fish, Heterandria formosa, and similar studies of poeciliid fish spanning a range of life histories are consistent with our hypothesis. Together these results suggest that sibling competition is a direct consequence of the evolution of matrotrophy and superfetation in poeciliid fish.     

The occurrence of spermatozoa in the ovary of the gynogenetic viviparous teleost Poecilia formosa (POECILIIDAE)

The reproductive mode of the female viviparous teleost Poecilia formosa (Poeciliidae) represents the phenomenon known as gynogenesis; that is, parthenogenetic development is initiated by spermatozoa which are needed for physiological activation of the egg and the initiation of gestation, but spermatozoa are prevented from contributing to the genome of the embryo. For the reason that no previous histological analyses of the ovary of this species during the reproductive cycle has been published the present study has been conducted. This study examined the histology of the ovary of P. formosa during nongestation and gestation phases and identified the presence of spermatozoa inside the ovary. Spermatozoa were observed in folds of the ovarian epithelium of P. formosa during both the nongestation and gestation phases. Sperm storage as documented in this study is a very important trait for the gynogenetic viviparous fish P. formosa contributing to the understanding of this species reproduction. J. Morphol. 277:341–350, 2016. © 2015 Wiley Periodicals, Inc.     

Oogenesis of microlecithal oocytes in the viviparous teleost Heterandria formosa

Viviparous teleosts exhibit two patterns of embryonic nutrition: lecithotrophy (when nutrients are derived from yolk that is deposited in the oocyte during oogenesis) and matrotrophy (when nutrients are derived from the maternal blood stream during gestation). Nutrients contained in oocytes of matrotrophic species are not sufficient to support embryonic development until term. The smallest oocytes formed among the viviparous poeciliid fish occur in the least killifish, Heterandria formosa, these having diameters of only 400 μm. Accordingly, H. formosa presents the highest level of matrotrophy among poeciliids. This study provides histological details occurring during development of its microlecithal oocytes. Five stages occur during oogenesis: oogonial proliferation, chromatin nucleolus, primary growth (previtellogenesis), secondary growth (vitellogenesis), and oocyte maturation. H. formosa, as in all viviparous poeciliids, has intrafollicular fertilization and gestation. Therefore, there is no ovulation stage. The full‐grown oocyte of H. formosa contains a large oil globule, which occupies most of the cell volume. The oocyte periphery contains the germinal vesicle, and ooplasm that includes cortical alveoli, small oil droplets and only a few yolk globules. The follicular cell layer is initially composed of a single layer of squamous cells during early previtellogenesis, but these become columnar during early vitellogenesis. They are pseudostratified during late vitellogenesis and reduce their height becoming almost squamous in full‐grown oocytes. The microlecithal oocytes of H. formosa represent an extreme in fish oogenesis typified by scarce yolk deposition, a characteristic directly related to matrotrophy. J. Morphol., 2011. © 2010 Wiley‐Liss, Inc.     

Superfetation increases total fecundity in a viviparous fish regardless of the ecological context

Superfetation is the ability of females to simultaneously carry multiple broods of embryos at different developmental stages. This is an uncommon reproductive strategy that has evolved independently several times in viviparous fishes. The ecological conditions that favor higher degrees of superfetation (the presence of more simultaneous broods) still remain unclear. In this study we tested hypotheses about the potential effects of three particular ecological factors (water flow velocity, population density, and adult mortality) on superfetation. We used data on six populations of one fish species from the family Poeciliidae (Poeciliopsis baenschi) and a multimodel inference framework to test these hypotheses. We found no clear associations between the degree of superfetation and these ecological factors. Instead, we found a positive relationship between the total number of embryos carried by females and superfetation. Females increased their total fecundity as they overlapped more broods and this pattern was independent of the particular ecological conditions. Thus, in P. baenschi superfetation may facilitate a greater reproductive output. In addition, this positive relationship between total number of embryos and superfetation was stronger in small- and medium-sized females, whereas large females produced few or no simultaneous broods regardless of their total fecundity. The observed lack of association between superfetation and ecological variables is noteworthy because previous studies on other congeneric species have found that superfetation may vary as a function of water flow velocity or food availability. Our results indicate that the effect of particular selective factors on the degree of superfetation may differ among closely related species.     

Have superfetation and matrotrophy facilitated the evolution of larger offspring in poeciliid fishes?

Superfetation is the ability of females to simultaneously carry multiple broods of embryos, with each brood at a different developmental stage. Matrotrophy is the post‐fertilization maternal provisioning of nutrients to developing embryos throughout gestation. Several studies have demonstrated that, in viviparous fishes, superfetation and matrotrophy have evolved in a correlated way, such that species capable of bearing several simultaneous broods also exhibit advanced degrees of post‐fertilization provisioning. The adaptive value of the concurrent presence of both reproductive modes may be associated with the production of larger newborns, which in turn may result in enhanced offspring fitness. In this study, we tested two hypotheses: (1) species with superfetation and moderate or extensive matrotrophy give birth to larger offspring compared with species without superfetation or matrotrophy; (2) species with higher degrees of superfetation and matrotrophy (i.e. more simultaneous broods and increased amounts of post‐fertilization provisioning) give birth to larger offspring compared with species with relatively low degrees of superfetation and matrotrophy (i.e. fewer simultaneous broods and lesser amounts of post‐fertilization provisioning). Using different phylogenetic comparative methods and data on 44 species of viviparous fishes of the family Poeciliidae, we found a lack of association between offspring size and the combination of superfetation and matrotrophy. Therefore, the concurrent presence of superfetation and moderate or extensive matrotrophy has not facilitated the evolution of larger offspring. In fact, these traits have evolved differently. Superfetation and matrotrophy have accumulated gradual changes that largely can be explained by Brownian motion, whereas offspring size has evolved fluidly, experiencing changes that probably resulted from selective responses to the local conditions.     

Maternal Effects on Offspring Quality in Poeciliid Fishes

SYNOPSIS. We evaluated the effects of maternal environment onoffspring size and composition in three species of poeciliidfishes. We chose food availability as the environmental factorfor study. Mature females were assigned to either high or lowfood for an interval of time, then randomly reassigned to highor low food, with the restriction that there be equal numbersin each of four treatments: high-high, high-low, lowhigh, andlow-low food availability. The three species chosen for studydiffer in the pattern of maternal provisioning. Poecilia reticulataand Priapichthys festae mothers provide all resources necessaryfor development as yolk, prior to fertilization. In contrast,Heterandria formosa mothers continue to provision the youngthroughout development. These species also differ in whetheror not they have superfetation, or the ability to carry multiplebroods of young in different stages of development. P. reticulatadoes not have superfetation while the other two species do.We were interested in whether the pattern of maternal provisioningor superfetation influenced the maternal effect. The two lecithotrophicspecies responded to low food by producing larger young withgreater fat reserves. H. formosa, the matrotrophic species,responded to low food by producing smaller young. We proposethat the production of large young in the face of low food availabilitymight represent adaptive plasticity; matrotrophy might representa constraint that prevents such an adaptive response. Superfetationhad no impact on this maternal effect.     

Habitat predicts reproductive superfetation and body shape in the livebearing fish Poeciliopsis turrubarensis

Superfetation, the ability of females to simultaneously carry more than one brood at different developmental stages, is an unusual reproductive strategy that has independently evolved several times in the livebearing fish family Poeciliidae. Why this strategy has evolved remains uncertain. One hypothesis is that superfetation is a response to selective pressures that constrain the physical space within a female in which her offspring can develop. This hypothesis is reasonable, because superfetation should reduce the total volume needed to house developing embryos – that is, fewer large, fully developed embryos will be held by a superfetating female (with several broods at different developmental stages) than a non‐superfetating female (where all embryos reach a fully developed stage at the same time). In this study, we explore this ‘morphological constraint’ hypothesis of superfetation by examining the livebearing fish, Poeciliopsis turrubarensis. We found that populations vary markedly in degree of superfetation, with individuals carrying from two to four distinct broods across different geographic areas. These populations also occupy a range of habitat types: some populations occur in slow moving coastal rivers near the ocean, while other populations occur far inland in fast moving waters that drain steep mountain environments. In comparing populations from these two types of environments, we find a strong association between stream habitat type and the degree of superfetation within populations. Fish from inland populations have higher levels of superfetation than their coastal counterparts. In addition, geometric morphometric analysis revealed that inland populations are also more fusiform than fish from coastal locations. Combined, these two lines of evidence support the ‘morphological constraint’ hypothesis, and suggest that the life history strategy of superfetation could be driven by environmental pressures that favor a more streamlined phenotype.     

Morphological structures for potential sperm storage in poeciliid fishes. Does superfetation matter?

Sperm storage within the female reproductive tract has been reported as a reproductive strategy in several species of vertebrates and invertebrates. However, the morphological structures that allow for sperm to be stored and kept viable for long periods are relatively unknown in osteichthyes. We use histological and stereological tools to identify and quantify sperm storage structures (spermathecae) in 12 species of viviparous Poeciliidae. We found spermathecae in nine species, six of which exhibit superfetation (the ability of females to simultaneously carry within the ovary two or more broods of embryos at different stages of development). These spermathecae are folds of ovarian tissue that close around spermatozoa. We compared the number and size (volume) of spermathecae between species with and without superfetation. Species that exhibit superfetation had a significantly higher number of spermathecae than species that do not exhibit this reproductive strategy. In addition, we found that the mean volume of spermathecae and total volume of spermathecae present in the ovary are marginally higher in species with superfetation. Our results contribute to the understanding of the morphological structures that allow for sperm storage in viviparous osteichthyes and suggest a positive relationship between superfetation and the capacity of females to store sperm.     

Egg Size, Intrinsic Competition, and Lethal Interference in the Parasitoids Encarsia pergandiella and Encarsia formosa

Recent population dynamic theory predicts that disruption of biological control may occur when one parasitoid species' superiority in intrinsic competition is associated with a lower ability to find and exploit hosts (i.e., ability in extrinsic competition). One might expect such a trade-off, for instance, if parasitoids with larger (and fewer) eggs are more likely to prevail in intrinsic competition than species with smaller (and more numerous) eggs. We tested the idea that relative egg size could be used to predict the outcome of intrinsic competition in two closely related endoparasitoids, Encarsia pergandiella Howard and Encarsia formosa Gahan. Contrary to expectation, the parasitoid species with smaller eggs, E. pergandiella, prevailed in intrinsic competition, regardless of the order that hosts were exposed to the two species. In a literature survey, we found four studies of competing pairs of endoparasitoid species for which: (a) egg size estimates were available and (b) one species was consistently superior in intrinsic competition. In three of the four studies, the small-egged species prevailed in intrinsic competition, as we also found. Although E. formosa lost in intrinsic competition, this species negatively affected E. pergandiella's progeny production by host feeding on and killing hosts containing E. pergandiella eggs. E. formosa females also host fed on conspecific-parasitized hosts. As a mechanism of both intra- and interspecific interference competition, host feeding on parasitized hosts contradicts assumptions about the nature of interference competition in existing population dynamics models.     

Colony social organization of <Emphasis Type="Italic">Lasioglossum malachurum</Emphasis> Kirby (Hymenoptera,Halictidae) in southern Greece

Summary We studied the nesting and social biology of two aggregations of the obligately eusocial halictine bee Lasioglossum malachurum at Agios Nikolaos Monemvasias (ANM) in southern Greece. Observations and nest excavations carried out from May to June 2000, revealed social and demographic variation between aggregations and years at ANM, as well as notable differences between these and other European populations. In southern Greece, the colony cycle includes multiple broods: the first two broods comprise only workers, whereas the third brood comprises workers, males, and gynes. Although pleometrosis is unknown in other populations, in the ANM region, as many as 10% of nests have more than one foundress. Newly emerged workers and gynes exhibit non-overlapping size distributions, but a few queens are worker-sized, indicating that workers occasionally overwinter and become foundresses. Although the vast majority of workers are unmated and most exhibit no ovarian development, an increase in worker ovarian development at the time of male production suggests that many males may develop from worker-laid eggs. Worker reproduction seems to be inhibited by the presence of queens, and annual variation in queen mortality may underlie annual variation in worker ovarian development. Across Europe, the major demographic and social differences among L. malachurum populations are in the number of worker broods and the extent of worker ovarian development. This contrasts with the results of a principal components analysis of social traits among 15 social L. (Evylaeus) populations, which shows that interspecific social variation is defined by the proportion of males in the early brood, the proportion of workers mated, queen-worker size dimorphism, gyne overwintering locale, and the proportion of workers with developed ovaries.Received 17 June 2002; revised 16 January 2002; accepted 27 January 2003.     

Developmental rates of two congeneric parasitoids,Encarsia formosa and E. pergandiella (Hymenoptera: Aphelinidae), utilizing different egg provisioning strategies

Endoparasitic Hymenoptera vary in the extent to which they provision their eggs and thus in the degree to which they appear to rely on their hosts for resources during embryonic development. In this study, developmental rates were examined in two congeneric parasitoid species, Encarsia formosa and E. pergandiella, that provision their eggs to different degrees. E. formosa eggs are much larger than E. pergandiella eggs. E. formosa eggs hatch significantly earlier than the eggs of E. pergandiella when deposited in 1st or 4th instar nymphs of a common whitefly host, Bemisia tabaci. Both species hatch earlier in 4th instar nymphs, but the delay in hatching in hosts parasitized as 1st instars is much greater in E. pergandiella. While E. formosa develops more rapidly to the 1st larval instar, E. pergandiella emerge as adults significantly earlier, though smaller, than E. formosa adults regardless of the host instar parasitized. These findings show that the extent of provisioning in the eggs of these wasps does not strictly determine their order of progression through different stages of development.     

Evidence of multiple paternity in the bluntnose klipfish, <Emphasis Type="Italic">Clinus cottoides</Emphasis> (Blennioidei: Clinidae: Clinini)

Clinids of the tribe Clinini are viviparous fishes occurring in the temperate waters of southern Africa. Females of the genus Clinus exhibit reproductive traits suggesting multiple paternity. These traits include prolonged gestation periods, matrotrophy and superfetation. We tested the hypothesis that broods of the species C. cottoides are sired by multiple males with the use of microsatellites. We genotyped three broods from known mothers and analysed the relationships within each brood using the software program COLONY, we also used allele counting to find evidence of multiple paternity. Our results revealed that multiple paternity occurred in all three broods analysed; two broods likely had two sires and one brood three sires. One male appear to have fathered offspring with separate females. Our study represents the first molecular analysis of parentage in C. cottoides.     

Annual reproductive cycle based on histological changes in the ovary of the female mosquitofish,Gambusia affinis, in central Japan

To clarify the annual reproductive cycle of wild female mosquitofish,Gambusia affinis, in Mie Prefecture, central Japan, changes in ovarian histology were investigated. Female mosquitofish kept in aquaria under constant temperature (25°C) and photoperiod (16L: 8D) conditions produced successive broods at intervals of 22.1±0.46 days (n=7). Between days 0–3 following parturition, females began active vitellogenesis. Between days 3–5, fully grown oocytes matured and were fertilized, and embryonic development began in the follicles. By day 10, as fertilized eggs continued embryonic development, some oocytes at the oil-droplet stage had begun to accumulate yolk globules for the next gestation. Thus, vitellogenesis of the succeeding batch of oocytes overlaps with gestation during reproduction in the mosquitofish. A rearing experiment showed the annual reproductive cycle of mosquitofish breeding in Nagashima to be as follows. Although oocytes had not at that point developed to the yolk globule stage, copulation occurred in February. Females began vitellogenesis in early May, the first pregnancy of the year commencing in mid-May. From mid-May to August, females repeated the gestation cycle (vitellogenesis, maturation, fertilization, pregnancy and parturition) at around one month intervals. In September, oocyte recruitment from the oil-droplet to the yolk globule stage ceased. After the final parturition, the ovaries contained only non-vitellogenic oocytes. Spermatozoa in the ovarian cavity were scare from November to January.     

Viviparity in the halfbeak genera Dermogenys and Nomorhamphus (Teleostei: Hemiramphidae)

Gravid ovaries were examined histologically from two species of Nomorhamphus and 21 populations of Dermogenys. In addition, changes in dry-weight throughout gestation are provided for 15 populations. The ovaries are paired organs running along the lateral body wall and are separated along most of their length. In all specimens examined, embryos are fertilized within the ovarian follicle. Viviparity in these species is divided herein into five categories designated types I–V. In types I and II the entire gestation period is intrafollicular, whereas in types III–V only the early stages of gestation are intrafollicular with the major period of development occurring in the ovarian lumen (intraluminal). Type I is characterized by the retention of a large amount of yolk throughout gestation. Superfetation is not observed. Populations of D. pusilla from Vietnam and Thailand decrease in dry-weight throughout gestation. This, coupled with the slight vascularization of the yolk sac, suggests strict lecithotrophy. Populations of D. pusilla from Singapore and Bangladesh undergo an increase in dry weight and exhibit an increased vascularization of the yolk sac, suggesting a form of unspecialized matrotrophy. Type II is characterized by a small amount of yolk, an expansion of the coelomic cavity and pericardial sac, and a simple cuboidal epithelium on the general body surfaces. Superfetation occurs with up to three broods present within a single ovary. Dermogenys pusilla from Sabah, D. orientalis and Dermogenys sp. (Sulawesi) exhibit the type II form of viviparity. Dermogenys vivipara from the eastern Philippine islands of Culion and Busuanga exhibit characteristics considered intermediate between type I and II. These results are compared with those from other viviparous species exhibiting intrafollicular gestation. In species with types III–V (intraluminal gestation), developing oocytes are restricted to a distinct ridge of ovigerous tissue extending along the entire length of the ovary. Two species, D. viviparus (Luzon, Philippines) and Dermogenys sp. (Luzon) have the type III form of viviparity. In this form, oocytes are small (0.8–1.0 mm) with little yolk reserves and embryos, covered with a simple cuboidal epithelium and possessing an expanded belly sac, are retained within the follicles until a late fin-bud stage. Type III embryos found within the ovarian lumen have a greatly expanded belly sac and remain covered by a simple cuboidal epithelium until parturition. Superfetation is present in these species with two broods observed simultaneously within a single ovary. Five species, D. megarrhamphus, D. weberi, D. viviparus (Jolo, Philippines), Nomorhamphus sp. (Sulawesi), and N. towoetii, were observed with the type IV form of viviparity. Embryos in this category are evacuated into the ovarian lumen prior to a fin-bud stage and retain a large yolk mass throughout development. Superfetation is absent in these species. A differentform of viviparity (type V) is present in D. ebrardtii in which embryos appear to obtain nutrients through a form of oophagy and aldelphophagy (feeding on developing oocytes or less-developed siblings). In all specimens with intraluminal development, atretic oocytes within the ovigerous ridge are abundant. These findings support the hypothesis that current species and generic limits may be artificial and underscores the potential of histological evidence for phylogenetic analysis of this group. J. Morphol. 234:295–317, 1997. © 1997 Wiley-Liss, Inc.     

Sitting ducklings: Timing of hatch,nest departure,and predation risk for dabbling duck broods

For ground‐nesting waterfowl, the timing of egg hatch and duckling departure from the nest may be influenced by the risk of predation at the nest and en route to wetlands and constrained by the time required for ducklings to imprint on the hen and be physically able to leave the nest. We determined the timing of hatch, nest departure, and predation on dabbling duck broods using small video cameras placed at the nests of mallard (Anas platyrhynchos; n = 26), gadwall (Mareca strepera; n = 24), and cinnamon teal (Anas cyanoptera; n = 5). Mallard eggs began to hatch throughout the day and night, whereas gadwall eggs generally started to hatch during daylight hours (mean 7.5 hr after dawn). Among all species, duckling departure from the nest occurred during daylight (98%), and 53% of hens typically left the nest with their broods 1–4 hr after dawn. For mallard and gadwall, we identified three strategies for the timing of nest departure: (a) 9% of broods left the nest the same day that eggs began to hatch (6–12 hr later), (b) 81% of broods left the nest the day after eggs began to hatch, and (c) 10% of broods waited 2 days to depart the nest after eggs began to hatch, leaving the nest just after the second dawn (27–42 hr later). Overall, eggs were depredated at 10% of nests with cameras in the 2 days prior to hatch and ducklings were depredated at 15% of nests with cameras before leaving the nest. Our results suggest that broods prefer to depart the nest early in the morning, which may best balance developmental constraints with predation risk both at the nest and en route to wetlands.     

Reproductive ecology of three ocypodid crabs II. Incubation sites and egg mortality

Mortality of eggs during incubation was estimated for three ocypodid crabs,Scopimera globosa, Ilyoplax pusillus andMacrophthalmus japonicus, and the influence of incubation sites was discussed. These crabs all lived in isolated burrows and fed on sediments during day time low tide.S. globosa andI. pusillus inhabited the upper intertidal sandflats, whereasM. japonicus inhabited the lower intertidal mudflats. Females of bothS. globosa andI. pusillus remained in their plugged burrows without feeding throughout incubation and the mortality of eggs was low despite large broods relative to body size. On the other hand, females ofM. japonicus fed actively on surface mud during incubation and the mortality of eggs was high despiite small broods relative to body size. InS. globosa andI. pusillus, the ovaries of ovigerous females were small until egg-hatching, whereas inM. japonicus, the ovaries grew rapidly during incubation and females were able to produce consecutive broods. I conclude that incubation of eggs in burrows may be advantageous in species which inhabit the upper interidal sandflats, even though the crabs cannot forage during incubation, since otherwise their eggs would be exposed to strong heat stress and desication during the summer. Furthermore, such species may produce few large broods because of less frequent interruption of feeding than that associated with production of many small broods.     

Proliferation of Oogonia and folliculogenesis in the viviparous teleost Ilyodon whitei (Goodeidae)

Oogonial proliferation in fishes is an essential reproductive strategy to generate new ovarian follicles and is the basis for unlimited oogenesis. The reproductive cycle in viviparous teleosts, besides oogenesis, involves development of embryos inside the ovary, that is, intraovarian gestation. Oogonia are located in the germinal epithelium of the ovary. The germinal epithelium is the surface of ovarian lamellae and, therefore, borders the ovarian lumen. However, activity and seasonality of the germinal epithelium have not been described in any viviparous teleost species regarding oogonial proliferation and folliculogenesis. The goal of this study is to identify the histological features of oogonial proliferation and folliculogenesis during the reproductive cycle of the viviparous goodeid Ilyodon whitei. Ovaries during nongestation and early and late gestation were analyzed. Oogonial proliferation and folliculogenesis in I. whitei, where intraovarian gestation follows the maturation and fertilization of oocytes, do not correspond to the late oogenesis, as was observed in oviparous species, but correspond to late gestation. This observation offers an example of ovarian physiology correlated with viviparous reproduction and provides elements for understanding the regulation of the initiation of processes that ultimately result in the origin of the next generation. These processes include oogonia proliferation and development of the next batch of germ cells into the complex process of intraovarian gestation. J. Morphol. 275:1004–1015, 2014. © 2014 Wiley Periodicals, Inc.     

Variation in predation pressure as a mechanism underlying differences in numerical abundance between populations of the poeciliid fish Heterandria formosa

We explored whether a variation in predation and habitat complexity between conspecific populations can drive qualitatively different numerical dynamics in those populations. We considered two disjunct populations of the least killifish, Heterandria formosa, that exhibit long-term differences in density, top fish predator species, and dominant aquatic vegetation. Monthly censuses over a 3-year period found that in the higher density population, changes in H. formosa density exhibited a strong negative autocorrelation structure: increases (decreases) at one census tended to be followed by decreases (increases) at the next one. However, no such correlation was present in the lower density population. Monthly census data also revealed that predators, especially Lepomis sp., were considerably more abundant at the site with lower H. formosa densities. Experimental studies showed that the predation by Lepomis gulosus occurred at a much higher rate than predation by two other fish and two dragonfly species, although L. gulosus and L. punctatus had similar predation rates when the amount of vegetative cover was high. The most effective predator, L. gulosus, did not discriminate among life stages (males, females, and juveniles) of H. formosa. Increased predation rates by L. gulosus could keep H. formosa low in one population, thereby eliminating strong negative density-dependent regulation. In support of this, changes in H. formosa density were positively correlated with changes in vegetative cover for the population with a history of lower density, but not for the population with a history of higher density. Our results are consistent with the hypothesis that the observed differences among natural populations in numerical abundance and dynamics are caused in part by the differences in habitat complexity and the predator community.     

Do density‐driven mating system differences explain reproductive incompatibilities between populations of a placental fish?

Matrotrophy, the provisioning of embryos between fertilization and birth, creates the potential for conflict between mothers and embryos over the level of maternal investment. This conflict is predicted to drive the evolution of reproductive isolation between populations with different mating systems. In this study, we examine whether density‐driven mating system differences explain the patterns of asymmetric reproductive isolation observed in previous studies involving four populations of the matrotrophic least killifish, Heterandria formosa. Minimum sire number reconstructions suggested that two populations characterized by low densities had lower levels of concurrent multiple paternity than two populations characterized by high densities. However, low levels of genetic variation in the low‐density populations greatly reduced our probability of detecting multiple mating in them. Once we took the lower level of genetic variation into account in our estimations, high levels of multiple paternity appeared the rule in all four populations. In the population where we had the greatest power of detecting multiple mating, we found that multiple paternity in H. formosa typically involves multiple sires contributing to offspring within the same brood instead of different fathers contributing to distinct, simultaneously provisioned broods. Paternity was often skewed towards one sire. Our results suggest that differences between H. formosa populations in the levels of multiple paternity are not sufficient to explain the reproductive isolation seen in previous studies. We suggest that other influences on maternal–foetal conflict may contribute to the pattern of reproductive isolation observed previously. Alternatively, the asymmetric reproductive isolation seen in previous studies might reflect the disruption of maternal–foetal coadaptation.