Mating systems are diverse in animals, notably in crustaceans, but can be inferred from a limited set of parameters. Baeza and Thiel (2007) proposed a model predicting mating systems of symbiotic crustaceans with three host characteristics and the risk of predation. These authors proposed five mating systems, ranging from monogamy to polygynandry (where multiple mating occurs for both genders). Using microsatellite loci, we tested the putatively mating system of the ectoparasite crab Dissodactylus primitivus. We determined the mating frequencies of males and females, parentage assignment (COLONY & GERUD software) as well as the contents of female spermathecae. Our results are globally consistent with the model of Baeza and Thiel and showed, together with previous aquarium experiments, that this ectoparasite evolved a polygamous mating system where males and females move between hosts for mate search. Parentage analyses revealed that polyandry is frequent and concerns more than 60% of clutches, with clutches being fertilized by up to 6 different fathers. Polygyny is supported by the detection of eight males having sired two different broods. We also detected a significant paternity skew in 92% of the multipaternal broods. Moreover, this skew is probably higher than the estimation from the brood because additional alleles were detected in most of spermathecae. This high skew could be explained by several factors as sperm competition or cryptic female choice. Our genetic data, combined with previous anatomic analyses, provide consistent arguments to suggest sperm precedence in D. primitivus.
Marine organisms in Antarctica are adapted to an extreme ecosystem including extremely stable temperatures and strong seasonality due to changes in day length. It is now largely accepted that Southern Ocean organisms are particularly vulnerable to global warming with some regions already being challenged by a rapid increase of temperature. Climate change affects both the physical and biotic components of marine ecosystems and will have an impact on the distribution and population dynamics of Antarctic marine organisms. To predict and assess the effect of climate change on marine ecosystems a more comprehensive knowledge of the life history and physiology of key species is urgently needed. In this study we estimate the Dynamic Energy Budget (DEB) model parameters for key benthic Antarctic species the sea star Odontaster validus using available information from literature and experiments. The DEB theory is unique in capturing the metabolic processes of an organism through its entire life cycle as a function of temperature and food availability. The DEB model allows for the inclusion of the different life history stages, and thus, becomes a tool that can be used to model lifetime feeding, growth, reproduction, and their responses to changes in biotic and abiotic conditions. The DEB model presented here includes the estimation of reproduction handling rules for the development of simultaneous oocyte cohorts within the gonad. Additionally it links the DEB model reserves to the pyloric caeca an organ whose function has long been ascribed to energy storage. Model parameters described a slowed down metabolism of long living animals that mature slowly. O. validus has a large reserve that—matching low maintenance costs- allow withstanding long periods of starvation. Gonad development is continuous and individual cohorts developed within the gonads grow in biomass following a power function of the age of the cohort. The DEB model developed here for O. validus allowed us to increase our knowledge on the ecophysiology of this species, providing new insights on the role of food availability and temperature on its life cycle and reproduction strategy.
Aim To describe and analyse asteroid biogeographic patterns in the Southern Ocean (SO) and test whether reproductive strategy (brooder versus broadcaster) can explain distribution patterns at the scale of the entire class. We hypothesize that brooding and broadcasting species display different biogeographic patterns.Location Southern Ocean, south of 45°S.Methods Over 14,000 asteroid occurrences are analysed using bootstrapped spanning network (BSN), non-metrical multidimensional scaling (nMDS) and clustering to uncover the spatial structure of faunal similarities among 25 bioregions.Results Main biogeographic patterns are congruent with previous works based on other taxa and highlight the isolation of New Zealand, the high richness in the Scotia Arc area particularly of brooding species, an East/West Antarctic differentiation, and the faunal affinities between South America and sub-Antarctic Islands. Asteroids show lower endemism levels than previously reported with 29% of species occurring in Antarctica only. In particular, asteroids from Tierra del Fuego showed affinities with those of West Antarctica at the species level, suggesting a recent mixing of assemblages. Biogeographic patterns are highly linked to reproductive strategy. Patterns also differ according to the taxonomic level, revealing the underlying role of historical factors.Main conclusions Patterns of sea star biogeography are consistent with results obtained for other marine groups and are strongly linked to reproductive strategy.
Species inventories are essential to the implementation of conservation policies to mitigate biodiversity loss and maintain ecosystem services and their value to the society. This is particularly topical with respect to climate change and direct anthropogenic effects on Antarctic biodiversity, with the identification of the most at-risk taxa and geographical areas becoming a priority. Identification tools are often neglected and considered helpful only for taxonomists. However, the development of new online information technologies and computer-aided identification tools provides an opportunity to promote them to a wider audience, especially considering the emerging generation of scientists who apply an integrative approach to taxonomy. This paper aims to clarify essential concepts and provide convenient and accessible tools, tips and suggested systems to use and develop knowledge bases (KBs). The software Xper3 was selected as an example of a user-friendly KB management system to give a general overview of existing tools and functionalities through two applications: the ‘Antarctic Echinoids’ and ‘Odontasteridae Southern Ocean (Asteroids)’ KBs. We highlight the advantages provided by KBs over more classical tools, and future potential uses are highlighted, including the production of field guides to aid in the compilation of species inventories for biodiversity conservation purposes.
The present dataset is a compilation of georeferenced occurrences of asteroids (Echinodermata: Asteroidea) in the Southern Ocean. Occurrence data south of 45°S latitude were mined from various sources together with information regarding the taxonomy, the sampling source and sampling sites when available. Records from 1872 to 2016 were thoroughly checked to ensure the quality of a dataset that reaches a total of 13,840 occurrences from 4,580 unique sampling events. Information regarding the reproductive strategy (brooders vs. broadcasters) of 63 species is also made available. This dataset represents the most exhaustive occurrence database on Antarctic and Sub-Antarctic asteroids.
The pinnotherid crab Dissodactylus primitivus lives parasitically on 2 burrowing echinoid species, Meoma ventricosa and Plagiobrissus grandis. The fecundity of female crabs varies between hosts, and is higher when parasitizing P. grandis than M. ventricosa. Moreover, the hosts present great variations in morphology (size and density of spines). These characteristics suggest the potential to differentiate crabs according to host species. We investigated the genetic (microsatellites) and morphometric (outline analysis) differentiation of this parasitic crab between 2 host species at 1 Jamaican site (Western Lagoon, Discovery Bay), and compared it with geographic differentiation among 4 sites along the north coast of Jamaica.Greater genetic differences between parasites of the 2 sympatric hosts than between parasites of a single host at different geographic locations would indicate host differentiation. Genetic analyses (microsatellites) did not detect spatial differentiation (probably due to local hydrography) or differentiation according to host species. This lack of host differentiation could be explained by mobility of adult crabs between hosts. However, there was weak but significant morphological differentiation between female crabs from the 2 hosts. This morphological difference may reflect constraints due to host morphology.
Poecilogony, or multiple developmental modes in a single species, is exceedingly rare. Several species described as poecilogenous were later demonstrated to be multiple (cryptic) species with a different developmental mode. The Southern Ocean is known to harbor a high proportion of brooders (Thorson's Rule) but with an increasing number of counter examples over recent years. Here we evaluated poecilogony vs. crypticism in the brittle star Astrotoma agassizii across the Southern Ocean. This species was initially described from South America as a brooder before some pelagic stages were identified in Antarctica. Reproductive and mitochondrial data were combined to unravel geographic and genetic variation of developmental modes. Our results indicate that A. agassizii is composed of seven well-supported and deeply divergent clades (I: Antarctica and South Georgia; II: South Georgia and Sub-Antarctic locations including Kerguelen, Patagonian shelf, and New Zealand; III-VI-VII: Patagonian shelf, IV-V: South Georgia). Two of these clades demonstrated strong size dimorphism when in sympatry and can be linked to differing developmental modes (Clade V: dwarf brooder vs. Clade I: giant broadcaster). Based on their restricted geographic distributions and on previous studies, it is likely that Clades III-VI-VII are brooders. Clade II is composed of different morphological species, A. agassizii and A. drachi, the latter originally used as the outgroup. By integrating morphology, reproductive, and molecular data we conclude that the variation identified in A. agassizii is best described as crypticism rather than poecilogony.
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