Broods Of Embryos Research Articles

In situ observation of external surface brooding by Clavularia cf. inflata (Octocorallia) on reefs of northwestern Okinawa Island, Japan

ABSTRACT The timing of larval production and release of organisms is important in understanding their presence and prevalence in the environment. On the subtropical coral reefs around Okinawa Island, Japan, the reproductive timing of many soft coral species is still largely unknown. In this study, we report the first documentation of in situ external brooding and planulae release of a stoloniferan octocoral observed on the coral reefs of Okinawa Island. We observe external brooding of embryos and developing larvae on the colony surface and the subsequent planulation of some azooxanthellate larvae of Clavularia cf. inflata from two coral reef sites in the northwestern region of Okinawa Island. These observations indicate that this species reproduces concurrently with other zooxanthellate coral reef anthozoans in the summer season.

Deep-sea ctenostome bryozoans: revision of the family Pachyzoidae, with description of a new genus and three new species from Zealandia

Pachyzoidae is a little-known family of deep-sea ctenostome Bryozoa that until now was monospecific for Pachyzoon atlanticum. Originally described from the Atlantic Ocean, the genus was also found off southeastern New Caledonia in deep waters of the geological continent of Zealandia. Pachyzoon atlanticum forms globular to flat round colonies, living on soft, muddy to sandy bottoms with a few rhizoidal cystid appendages extending from the basal, substrate-oriented side. In this study, we investigate additional pachyzoids, collected between 1965 and 2015 from over 40 sites around New Zealand, by means of detailed morphological and histological investigations. In total, several hundred colonies were encountered in the NIWA Invertebrate Collection, comprising two new species of the genus Pachyzoon, P. grischenkoi sp. nov. and P. pulvinaris sp. nov., and the new genus and species Jeanloupia zealandica gen. et sp. nov.. The genus Jeanloupia is characterized by small disc-shaped colonies with highly elongated peristomes and a quadrangular aperture, distinct from the round apertures of the genus Pachyzoon. Pachyzoid species differ in colony structure and shape, apertural papillae and polypide features such as tentacle number or digestive-tract details. Cystid appendages are non-kenozooidal, but may originate from laterally flanking kenozooids. Based on published images, alleged P. atlanticum from New Caledonia is re-interpreted as P. pulvinaris n. sp.. Morphological characters support alcyonidioidean relationships, as previously suggested. First observations on pachyzoid reproduction show macrolecithal oocytes and brooding of embryos, which seems to be the general pattern for this family. The occurrence of three new Zealandian species in a comparatively small geographical area far from the Atlantic indicates a high possibility of more species to discovered.

Protandric simultaneous hermaphroditism inSalmoneus carvachoiAnker, 2007 (Decapoda: Alpheidae): a new sexual system in alpheid shrimps

AbstractIn caridean shrimps, sexual systems vary from gonochorism to various forms of hermaphroditism. The shrimp Salmoneus carvachoi has been reported to exhibit both male (appendix masculina) and female (brooding embryos) anatomical characteristics simultaneously. Our aim was to examine the sexual system of S. carvachoi and to test the hypothesis of protandric simultaneous hermaphroditism (PSH) in this species. We analysed internal and external features using microscopy and histology techniques. Our analyses support the hypothesis of PSH in S. carvachoi and enabled the identification of male-phase and hermaphroditic individuals. All individuals exhibit a well-developed appendix masculina on the endopods of the second pleopods; however, small male-phase individuals possess only male gonopores, whereas larger hermaphroditic individuals possess both female and male gonopores. Hermaphrodites exhibit both male and female germinative cells in various stages of development, as well as an androgenic gland. Our study describes a novel sexual system for alpheids and provides a detailed description of anatomical traits in S. carvachoi. Studies that describe sexual systems in Alpheidae may shed light on the evolutionary history of gender expression in carideans and how environmental conditions favour sex allocation in decapods and other invertebrates.

Stay in shape: Assessing the adaptive potential of shell morphology and its sensitivity to temperature in the invasive New Zealand mud snail Potamopyrgus antipodarum through phenotypic plasticity and natural selection in Europe.

Climate change may force organisms to adapt genetically or plastically to new environmental conditions. Invasive species show remarkable potential for rapid adaptation. The ovoviviparous New Zealand mud snail (NZMS), Potamopyrgus antipodarum, has successfully established across Europe with two clonally reproducing mitochondrial lineages since its arrival in the first half of the 19th century. Its remarkable variation in shell morphology was shown to be fitness relevant. We investigated the effects of temperature on shell morphology across 11 populations from Germany and the Iberian Peninsula in a common garden across three temperatures. We analyzed size and shape using geometric morphometrics. For both, we compared reaction norms and estimated heritabilities. For size, the interaction of temperature and haplotype explained about 50% of the total variance. We also observed more genotype by environment interactions indicating a higher degree of population differentiation than in shape. Across the three temperatures, size followed the expectations of the temperature‐size rule, with individuals growing larger in cold environments. Changes in shape may have compensated for changes in size affecting space for brooding embryos. Heritability estimates were relatively high. As indicated by the very low coefficients of variation for clonal repeatability (CV A ), they can probably not be compared in absolute terms. However, they showed some sensitivity to temperature, in haplotype t more so than in z, which was only found in Portugal. The low CV A values indicate that genetic variation among European populations is still restricted with a low potential to react to selection. A considerable fraction of the genetic variation was due to differences between the clonal lineages. The NZMS has apparently not been long enough in Europe to accumulate significant genetic variation relevant for morphological adaptation. As temperature is obviously not the sole factor influencing shell morphology, their interaction will probably not be a factor limiting population persistence under a warming climate in Europe.

Unravelling another mystery: Parasite escape and host‐switching vary spatially in non‐indigenous populations of Japanese mystery snails

Abstract Due to anthropogenic mechanisms, global freshwater biodiversity is declining, and non‐indigenous species are consistently cited as a major threat to native ecosystems. In particular, exotic freshwater gastropods and their parasites have invaded ecosystems through deliberate introductions and/or accidental transfer. In many cases, introduced hosts experience parasite escape in their non‐indigenous range by leaving behind some of their native parasite load during introduction. We investigated whether the Japanese mystery snail, Heterogen japonica, may be exhibiting signatures of parasite escape in non‐indigenous populations in the mid‐Atlantic U.S.A. by comparing the prevalence and diversity of trematode parasites in H. japonica and co‐occurring indigenous snails. Because trematodes can severely impact snail host reproduction, they are an important parasite group to investigate using comparative parasite analyses. Finally, we used genetic data to elucidate whether host switching of trematode lineages had occurred among the indigenous and non‐indigenous snails. Six locations from Richmond, Virginia to Washington, D.C. were surveyed for non‐indigenous and indigenous snails in 2018 and 2019. A random subset of each species was measured, dissected, sexed, and examined for parasite diversity. Brooding embryos were also counted in non‐indigenous snails. Among all snails, native species had a higher diversity of trematode (digenean and aspidogastrean) parasites than the invasive mystery snail, and infection was also influenced by site. Although H. japonica was uninfected at the majority of sites, it had moderate prevalence (up to 34%) of aspidogastrean trematodes at two sites. Female H. japonica infected with aspidogastreans had significantly fewer brooding embryos than uninfected snails. We found additional associates such as ciliates, nematodes, and the oligochaete Chaetogaster sp. in indigenous snails; of these, only ciliates and nematodes were found in association with H. japonica at comparatively low prevalence. While H. japonica has escaped several trematode species, specific populations still had high prevalence of aspidogastreans, the highest of which was found where H. japonica co‐occurred with the indigenous snail Elimia virginica. Genetic data found at least two cryptic lineages of aspidogastreans, and one was shared between H. japonica and E. virginica, suggesting that host‐switching has occurred. Parasites can play powerful roles in interspecific relationships, influence species interactions, and even impact ecosystem functioning. The ability of parasites to host switch could further influence community interactions in this system, particularly if H. japonica continues to spread in North America. Further research is needed to evaluate how parasites (or lack thereof) may mediate the interactions and demographics of indigenous and non‐indigenous species in invaded ranges.

Rhynchospioaciliata sp. nov., a new spionid species (Annelida, Spionidae) from the Korea Strait.

A new spionid polychaete, Rhynchospioaciliata sp. nov., was discovered in the fine sandy sediments of an intertidal habitat from Korean waters. The new species is considered a simultaneous hermaphrodite, but no brooding embryos were found in any of the specimens collected in this study. This species is unique in the absence of ciliation in the anteriormost chaetigers. Rhynchospioaciliata sp. nov. is morphologically most similar to Rhynchospiofoliosa Imajima, 1991 from Japan in having an elevation on the prostomium, conspicuously large and foliaceous branchiae, and intersegmental lateral pouches. However, the new species differs from the latter by the following characteristics: (1) large and lanceolate notopodial postchaetal lamellae of chaetiger 1, (2) transverse ciliated bands and ciliation on the inner branchiae absent in anteriormost chaetigers, and (3) pygidium with one pair of ventral cirri and numerous elongated dorsolateral cirri. Detailed description and illustrations of the new species are provided with molecular information on mitochondrial cytochrome c oxidase subunit I (COI), 16S ribosomal DNA (rDNA), nuclear 18S rDNA, and 28S rDNA.

Small sizes, big strategies: the relationship between female size, matrotrophy and superfetation throughout the reproductive lives of poeciliid fishes

AbstractIn viviparous fishes, females of species that exhibit matrotrophy (post‐fertilization maternal provisioning to developing embryos) and superfetation (ability of females to bear simultaneously multiple broods of embryos at distinct developmental stages) increase less in mass and volume during pregnancy than females of species that lack these traits. Such a reduction in reproductive allocation may provide greater benefits to young and small females for two reasons. First, they could devote energy and resources to both growth and reproduction. Second, they could compensate for the space restrictions that are inherent to a small body size because both superfetation and matrotrophy maximize fecundity for any given ovarian volume. In this study, we test the hypothesis that both matrotrophy and superfetation will decrease over female reproductive lifespan (i.e. as they grow larger). We examined reproductive females from 77 populations of 13 species of the family Poeciliidae. Remarkably, we found support for the matrotrophy prediction in only three populations. As expected, in these populations, small females were more matrotrophic than larger females, which in turn exhibited a predominantly lecithotrophic strategy. In one population, we found the opposite pattern—the degree of matrotrophy actually increased in larger females. With respect to superfetation, none of the populations showed a pattern consistent with our prediction. In fact, in five populations the pattern was opposite to our expectation—larger females produced more simultaneous broods than smaller females. Our findings reveal that the degree of matrotrophy and superfetation can vary throughout the adult lifespans of poeciliid fishes, but such ontogenetic shifts are not common in natural populations.

Behaviour, physiology and body mass of Nigerian indigenous hens during brooding

Abstract This study was conducted to investigate the behaviour, selected physiological indicators and body mass changes in Nigerian indigenous broody hens. The times spent by the hens sitting on eggs and on ingestive behaviours (feeding and drinking) were monitored between 14:00 and 18:00 h twice per week for three weeks. The growth and physiological indicators monitored were body mass, rectal temperature, breast temperature and blood glucose concentration. Data collected were analysed using repeated measures ANOVA of SPSS having week as the repeated factor. The time spent by hens sitting on the eggs (88.09 ± 5.38 – 92.91 ± 2.35 %) and on ingestive behaviours (0.06 ± 0.03 – 0.11 ± 0.07 %) were similar at the 1st, 2nd and 3rd week of brooding. The blood glucose concentration was reduced at the 1st and 2nd but increased at the 3rd week while the breast temperature (BT) increased at the 1st and 2nd but dropped at the 3rd week. The rectal temperature and body mass did not differ significantly (P > 0.05) during the three weeks of the brooding process. In conclusion, natural brooding of embryos by hens under tropical conditions was accompanied by changes in body metabolism required for generation of heat which is transferred through the breast region of the hens to the eggs without necessarily resulting in higher rectal temperature of the hens.

Social structure, sexual dimorphism and relative growth in the ghost shrimp Callichirus seilacheri (Bott, 1955) (Decapoda, Axiidea, Callianassidae) from the tropical eastern Pacific

ABSTRACTWe analyzed the social structure, sexual dimorphism and relative growth in the burrowing shrimp Callichirus seilacheri from the tropical eastern Pacific. To this end, 456 individuals of C. seilacheri were collected during monthly sampling from December 2011 to November 2012. No shrimp pairs or burrows inhabited by more than one shrimp were detected during the study period. Males were significantly smaller than females, denoting sexual dimorphism with respect to body size. In many juvenile males and females, the size of the right and left claws was the same, whereas in others the largest cheliped was located on the right or left side. Analysis of allometric growth between cheliped carpus length and cephalothorax length revealed an isometric relationship in juveniles of both sexes and adult females and positive allometric growth in adult males. The adjustment of the above relationship by the Somerton's method, denoted the existence of two main phases of growth related to sexual maturity, with transition points between juvenile and adult phase at 12.3 mm and 12.0 mm of body size for males and females, respectively. The observations on social structure, sexual dimorphism and relative growth of C. seilacheri argued that this species is polygamous. Furthermore, the high frequency of solitary females found brooding embryos suggested that males might roam among galleries in search of receptive females.

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.

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.

REPRODUCTIVE CYCLE, GAMETOGENESIS AND EMBRYONIC DEVELOPMENT OF NITIA TERETIUSCULA (BIVALIVA: UNIONIDAE), FROM THE RIVER NILE, AT SOHAG GOVERNORATE, EGYPT

The present study dealt with the description of the reproductive and gametogenic cycles and the embryonic development of the freshwater mussel Nitia teretiuscula from the River Nile. Macro and micro-anatomy showed that the present species is dioceous and gonadosomatic indices showed that the species is semiannual and had two gonadal growth periods, a short period of gonadal growth from January to March and a long period from April to August. Visceral indices revealed a reciprocal relationship with the gonadosomatic indices of both the two sexes. The recorded sex ratio of females to males was (1.5: 1). The oogenesis displayed five developmental stages; oogonia, previtellogenic oocytes, vitellogenic oocytes, late vitellogenic oocytes and mature ova. Also, spermatogenesis illustrated five developmental stages: spermatogonia, primary spermatocytes, and secondary spermatocytes, spermatids; which clustered to form sperm morula and finally metamorphosed to spermatozoa. Within the gills of females (marsupia), brooding of embryos was occurred till the formation of glochidia larvae. The unfertilized eggs were released from the gonads with distinct germinal vesicle. The fertilized eggs had two polar bodies and a fertilization cone. Successive cleavages were observed. Spiral cleavage, non-ciliated blastula and D-shaped larvae were recorded.

Costs and Benefits to Pregnant Male Pipefish Caring for Broods of Different Sizes.

Trade-offs between brood size and offspring size, offspring survival, parental condition or parental survival are classic assumptions in life history biology. A reduction in brood size may lessen these costs of care, but offspring mortality can also result in an energetic gain, if parents are able to utilize the nutrients from the demised young. Males of the broad-nosed pipefish (Syngnathus typhle) care for the offspring by brooding embryos in a brood pouch. Brooding males can absorb nutrients that emanate from embryos, and there is often a reduction in offspring number over the brooding period. In this study, using two experimentally determined brood sizes (partially and fully filled brood pouches), we found that full broods resulted in larger number of developing offspring, despite significantly higher absolute and relative embryo mortality, compared to partial broods. Male survival was also affected by brood size, with males caring for full broods having poorer survival, an effect that together with the reduced embryo survival was found to negate the benefit of large broods. We found that embryo mortality was lower when the brooding males were in good initial condition, that embryos in broods with low embryo mortality weighed more, and surprisingly, that males in higher initial condition had embryos of lower weight. Brood size, however, did not affect embryo weight. Male final condition, but not initial condition, correlated with higher male survival. Taken together, our results show costs and benefits of caring for large brood sizes, where the numerical benefits come with costs in terms of both embryo survival and survival of the brooding father, effects that are often mediated via male condition.

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 to 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 to 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 likely resulted from selective responses to the local conditions.

Reproduction, growth and early life history of the Antarctic gammarid amphipod Paramoera walkeri

The gammarid Paramoera walkeri is one of the most abundant amphipods in near-shore Antarctic waters. There has been increasing interest in P. walkeri as a test species for ecotoxicology studies and bio-monitoring for contaminants in Antarctica, but further information is needed to improve understanding of its biology including reproduction, growth and early life history. Female P. walkeri brooding late-stage embryos were collected in summer from coastal waters in the Vestfold Hills region, East Antarctica, and were maintained in the laboratory. Timing of neonate release, brood size and early post-marsupial survival and growth (total length) of juveniles were recorded. Brood size ranged from 26 to 86 neonates per female, and juvenile survival rates were high (96 %). The increase in body length of juveniles ranged from 0.017 to 0.043 mm/day with a mean growth rate of 0.028 mm/day (0.94 % per day) over 11 weeks with strong evidence for exponential growth over time. The body lengths of laboratory-raised juveniles were not significantly different to those of wild-caught juveniles with the same number of segments (15) in the first antennae, indicating that growth may have progressed at a similar rate in vivo and in situ. Juvenile growth was similar when modelled over time or by addition of first antennal segments. This study provides new information on the reproductive biology and early life history of P. walkeri, with further evidence that Antarctic amphipods exhibit slow growth, even when food is not a limiting factor, compared with species from lower latitudes.

Brooding strategy in fluctuating salinity environments: oxygen availability in the pallial cavity and metabolic stress in females and offspring in the Chilean oyster Ostrea chilensis.

Organisms that encounter stressful situations in nature often cope using behavioral (e.g., avoidance) or physiological tactics. In sessile mollusks, the only available behavioral option in dealing with salinity stress is to "clam up", isolating their tissues from the environment. Though effective in the short term, prolonged isolation can have detrimental physiological consequences, particularly for females brooding embryos in a mantle cavity that is isolated from the external environment. In the Quempillén estuary, the Chilean oyster, Ostrea chilensis, spent nearly one-third of its brooding season at salinities low enough to cause female isolation. When females thus isolated themselves, the dissolved oxygen in their mantle cavity fluid dropped to hypoxic levels within 10 min. In females that were brooding embryos, this depletion of oxygen was not uniform: oxygen was depleted more quickly in the palp region (where embryos accumulate) than in the inhalant region. Additionally, oxygen was reduced even more quickly in the palp region when females were brooding late-stage embryos, which consumed oxygen significantly more quickly than embryos in earlier developmental stages. Finally, O. chilensis used anaerobic metabolism to cope with the hypoxia induced by isolation, as lactate accumulated in the tissues of both females (brooding > non-brooding) and embryos (late stage > early stage). Our findings demonstrate the trade-off between an adaptive avoidance behavior (clamming up) and the potentially detrimental consequences brought on by such a behavior (hypoxia). Cycling of embryos throughout the mantle cavity by deliberate female pumping keeps them from accumulating in the area between the palps, forestalling the creation of hypoxic conditions there. In addition, the capacity for anaerobic metabolism by both females and their embryos should help them tolerate the low oxygen levels that do eventually arise when the pallial cavity is isolated from the surrounding environment during long periods of reduced ambient salinity.

The sexual and mating system of the shrimp Odontonia katoi (Palaemonidae, Pontoniinae), a symbiotic guest of the ascidian Polycarpa aurata in the Coral Triangle.

Theory predicts that monogamy is adaptive in symbiotic crustaceans inhabiting relatively small and morphologically simple hosts in tropical environments where predation risk away from hosts is high. We tested this prediction in the shrimp Odontonia katoi, which inhabits the atrial chamber of the ascidian Polycarpa aurata in the Coral Triangle. Preliminary observations in O. katoi indicated that males were smaller than females, which is suggestive of sex change (protandry) in some symbiotic organisms. Thus, we first investigated the sexual system of O. katoi to determine if this shrimp was sequentially hermaphroditic. Morphological identification and size frequency distributions indicated that the population comprised males that, on average, were smaller than females. Gonad dissections demonstrated the absence of transitional individuals. Thus, O. katoi is a gonochoric species with reverse sexual dimorphism. The population distribution of O. katoi in its ascidian host did not differ significantly from a random distribution and shrimps inhabiting the same host individual as pairs were found with a frequency similar to that expected by chance alone. This is in contrast to that reported for other socially monogamous crustaceans in which pairs of heterosexual conspecifics are found in host individuals more frequently than expected by chance alone. Thus, the available information argues against monogamy in O. katoi. Furthermore, that a high frequency of solitary females were found brooding embryos and that the sex ratio was skewed toward females suggests that males might be roaming among hosts in search of receptive females in O. katoi. Symbiotic crustaceans can be used as a model system to understand the adaptive value of sexual and mating systems in marine invertebrates.

In hot and cold water: differential life-history traits are key to success in contrasting thermal deep-sea environments.

Summary Few species of reptant decapod crustaceans thrive in the cold‐stenothermal waters of the Southern Ocean. However, abundant populations of a new species of anomuran crab, Kiwa tyleri, occur at hydrothermal vent fields on the East Scotia Ridge.As a result of local thermal conditions at the vents, these crabs are not restricted by the physiological limits that otherwise exclude reptant decapods south of the polar front.We reveal the adult life history of this species by piecing together variation in microdistribution, body size frequency, sex ratio, and ovarian and embryonic development, which indicates a pattern in the distribution of female Kiwaidae in relation to their reproductive development.High‐density ‘Kiwa’ assemblages observed in close proximity to sources of vent fluids are constrained by the thermal limit of elevated temperatures and the availability of resources for chemosynthetic nutrition. Although adult Kiwaidae depend on epibiotic chemosynthetic bacteria for nutrition, females move offsite after extrusion of their eggs to protect brooding embryos from the chemically harsh, thermally fluctuating vent environment. Consequently, brooding females in the periphery of the vent field are in turn restricted by low‐temperature physiological boundaries of the deep‐water Southern Ocean environment. Females have a high reproductive investment in few, large, yolky eggs, facilitating full lecithotrophy, with the release of larvae prolonged, and asynchronous. After embryos are released, larvae are reliant on locating isolated active areas of hydrothermal flow in order to settle and survive as chemosynthetic adults. Where the cold water restricts the ability of all adult stages to migrate over long distances, these low temperatures may facilitate the larvae in the location of vent sites by extending the larval development period through hypometabolism.These differential life‐history adaptations to contrasting thermal environments lead to a disjunct life history among males and females of K. tyleri, which is key to their success in the Southern Ocean vent environment.We highlight the complexity in understanding the importance of life‐history biology, in combination with environmental, ecological and physiological factors contributing to the overall global distribution of vent‐endemic species.

Population distribution, sexual dimorphism, and reproductive parameters in the crab Pinnixa valdiviensis Rathbun, 1907 (Decapoda: Pinnotheridae), a symbiont of the ghost shrimp Callichirus garthi (Retamal, 1975) in the southeastern Pacific

Pinnixa valdiviensis Rathbun, 1907 inhabits burrows of the ghost shrimp Callichirus garthi (Retamal, 1975) in the south-eastern Pacific. We described the host-use pattern and sexual dimorphism of P. valdiviensis to test for monogamy considering that the few other studied species of Pinnixa White inhabit their respective hosts as male-female pairs. Against expectations, P. valdiviensis lived either solitarily, or in small groups of up to four individuals; only a few burrows were inhabited by two crabs (either male-female or female-female pairs). The observations above argue against the notion that P. valdiviensis is monogamous. Furthermore, that a high frequency of solitary females were found brooding embryos and that the population sex ratio was skewed toward females suggests that males might roam among hosts in search of receptive females. We argue in favour of additional long-term (seasonal, >1 year) descriptive and experimental studies to reveal the mating tactics used by both males and females of P. valdiviensis. We also examined individual-level reproductive parameters in the studied species as little is known about reproduction in symbiotic crabs. Fecundity varied between 383 and 1052 eggs crab−1 with a mean ± SD of 774 ± 160 eggs crab−1 and increased significantly with female body size. Embryo volume varied between 0.0169 and 0.0443 with a mean ± SD of 0.0222 ± 0.0063 mm3 and did not vary with female body size. Reproductive output (RO) represented a mean ± SD of 5.74% ± 0.86% of crab body dry weight and increased proportionally with crab body weight. The RO in P. valdiviensis is lower than that reported for other free-living and symbiotic crabs.

Observations on the life history of a rare shrimp, Salmoneus carvachoi (Crustacea: Caridea: Alpheidae), a possible simultaneous hermaphrodite

This study reports on the life history of a rare alpheid shrimp,Salmoneus carvachoi, in the tropical western Atlantic. At an intertidal flat in Pontal Bay, Ilhéus, Bahia, north-eastern Brazil,S. carvachoiwas collected from within burrows of the axianassid mud shrimpAxianassa australisand the caridean snapping shrimpsAlpheus estuariensisandAlpheus chacei. These and earlier studies that reportedS. carvachoiin dwellings constructed by other larger burrowing crustaceans suggest thatS. carvachoiis a generalist species that establishes facultative symbiotic partnerships with larger burrowing decapods. We collected a total of 52 individuals during the sampling period (1 year); 19 (36.5%) of these shrimps carried embryos underneath the abdomen. The mean ± SD carapace length was 4.7 ± 0.7 and 5.5 ± 0.3 mm in non-brooding and brooding shrimps, respectively. All collected specimens, whether or not brooding embryos, bear appendices masculinae on the endopods of the second pleopods. Burrows harboured only one or two shrimps and never three or more shrimps. Pairs of shrimp that inhabited burrows consisted of two brooding shrimps (N = 3 pairs), two non-brooding shrimps (N = 3), or one brooding and one non-brooding shrimp (N = 1). The presence of appendices masculinae in all collected shrimps, whether or not brooding embryos, and the pairing of brooding shrimp within host burrows suggest thatS. carvachoiis a simultaneously hermaphroditic species.