Kristin M. Hultgren

Une nouvelle espèce eusociale de crevette pistolet, Synalpheus idelisae n. sp. (Decapoda, Alpheidae), avec une révision de la différenciation des castes chez les crevettes eusociales. Les crevettes pistolet du genre Synalpheus Spence Bate, 1888 sont les seuls organismes marins connus pour être eusociaux, c'est à dire présenter une structure sociale caractérisée par la vie en colonie et une division du travail en matière de reproduction. Nous décrivons ici une nouvelle espèce de crevette pistolet eusociale vivant dans les éponges, Synalpheus idelisae n. sp., à partir de spécimens collectés à Porto Rico et en République dominicaine. Les analyses phylogénétiques (basées sur les loci mitochondriaux 16S et COI) et les caractères morphologiques placent S. idelisae n. sp. au sein du complexe d'espèces Synalpheus rathbunae Coutière, 1909, qui comprend plusieurs autres espèces eusociales. Synalpheus idelisae n. sp. se distingue de ses proches parents par la forme de l'épine antérodorsale de la grande pince, la morphologie des pleures et le nombre de peignes de soies sur le cinquième péréiopode. Comme de nombreuses autres espèces eusociales du genre Synalpheus, S. idelisae n. sp. présente des caractéristiques telles qu'un développement larvaire direct et un second péréiopode à carpe quadrisegmenté. Notamment, nous décrivons plusieurs colonies de S. idelisae n. sp. où les reines possèdent, à la place de la grande pince, une seconde pince mineure, un schéma lié à la différenciation morphologique des castes chez les crevettes du genre Synalpheus. Enfin, nous examinons la fréquence de ce schéma chez d'autres espèces eusociales et présumées eusociales du genre Synalpheus. Avec l'ajout de S. idelisae n. sp., le complexe d'espèces S. rathbunae de l'Atlantique Ouest compte désormais sept espèces eusociales.

Studies on genome size (GS) aim to quantify the amount of DNA in an organism’s genome. Crustaceans are an excellent group in which to study GS from an evolutionary perspective since they are ubiquitous in almost all environments and show substantial variation in genome size. We evaluated the range of GS across two shrimp groups (Decapoda), focusing on differences in GS with different reproductive and developmental backgrounds. We also mapped GS as related to phylogeny to examine how nuclear DNA content changes in these two major groups of decapods. The most basal group, the Dendrobranchiata (represented by the superfamily Penaeoidea, with 14 species evaluated) had low GS values ranging 1.56–5.23 picograms. This group also has the most ancestral development mode, hatching as nauplius and following and extended pattern in what we refer to as “regular development.” By contrast, Pleocyemata, represented by the most derived shrimp taxa from infraorder Caridea (77 species evaluated), exhibits a variable set of GS values, ranging 3.71–22.40 picograms. This group undergoes a more advanced, shortened developmental mode, hatching as a zoea or even as an advanced zoea. We propose a relationship between the type of development, phylogenetic position, and genome size, where the basal group exhibiting the most wide-ranging type of development, showing lower GS values. More derived groups, which tend to have a shorter developmental mode, exhibit more plastic GS values and higher genome sizes reported in the literature.

Snapping shrimps in the genus Alpheus Fabricius, 1798 have long been a model system in which to study symbiotic relationships, especially the mutualism between burrowing shrimps and goby fishes. There has never been a comprehensive worldwide phylogeny of goby-dwelling snapping shrimp, however, hindering evolutionary studies of these symbioses. We examine phylogenetic relationships in the Alpheus brevirostris (Olivier, 1811) group, which is comprised of primarily burrowing species of snapping shrimps, many of which live in mutualistic partnership with gobies, and contains many of the most well-studied taxa in goby-shrimp symbioses. We first delimited cryptic species using COI data, which indicated multiple cryptic species of Alpheus. We then constructed a multi-locus phylogeny of species in the A. brevirostris group and several closely related species of Alpheus, and used fossil and transisthmian calibration points to construct a chronogram and date the origins of major clades. Our phylogeny confirmed previous work indicating the A. brevirostris group was paraphyletic, grouping in three major clades which diverged between 11.2 to 16.9 mya. Together, these data provide a phylogenetic framework for future taxonomic and evolutionary work on the origins and extent of the shrimp-goby and shrimp-echiuran symbioses.

Aim: We studied the niche evolution and diversification modes in transisthmian Alpheus shrimps by examining the interplay between environmental niche divergence and conservatism in allopatric sister species. In a broader perspective, the current study analysed the evolution of climatic niche and the role of the environment in species diversification of Alpheus transisthmian shrimp. Location: Atlantic and Eastern‐Pacific oceans. Taxon: Alpheus shrimps (Caridea: Alpheidae). Methods: We assembled georeferenced occurrences for 33 species of Alpheus (with 24 sister species) from a time‐calibrated molecular phylogeny. We modelled their ecological niches and assessed niche overlap through pairwise comparisons. Additionally, we performed phylogenetic reconstructions of the ancestral environmental niche, for each niche axis. Results: Our results demonstrate that thermal tolerances, food availability and hydrodynamic forces were relevant environmental axes in evolutionary processes in transisthmian species of Alpheus . Among the 528 paired comparisons, we found that most niches were divergent, including in 12 clades formed by pairs of sister species (in only two of these clades were the niches fully equivalent). Phylogenetic reconstructions of ancestral niches showed an initial niche conservatism in all axes, with divergences intensifying in the last 12 million years. Main Conclusions: We found evidence that confirms the relevance of the environmental changes that occurred in the West Atlantic and East Pacific for niche evolution in transisthmian Alpheus species, as well as for the emergence of some lineages. Our findings provide evidence for different modes of Alpheus species speciation in a period consistent with the closure of the Isthmus of Panama.

The alpheid snapping shrimp genus Synalpheus Spence Bate, 1888, is a prominent component of arthropod diversity found in coral reefs. Notably, Synalpheus is the only genus of marine organisms known to exhibit eusocial behavior. Although eusociality has evolved at least four times independently in Synalpheus, all described eusocial species are from the West Atlantic, with only a single study documenting possibly eusocial species from Indonesia. In 2008, during an expedition to Madagascar organized by the Florida Museum of Natural History (FLMNH), a diverse array of sponge-dwelling species was collected, including two species of Synalpheus exhibiting colonial behavior. Through detailed examination of these specimens, we have confirmed that these two species are eusocial and represent new eusocial species of Synalpheus outside of the West Atlantic. Consequently, we provide the first official documentation of eusocial species from the Western Indian Ocean and present their taxonomic descriptions and their phylogenetic relationships with other species of the genus in this study.

Snapping shrimps of the genus Alpheus Fabricius, 1798 exhibit remarkable diversity, with over 300 described species. The genus is well-known for its prevalence of species complexes, necessitating the need of new tools to facilitate species discrimination. Traditional taxonomic methods in Alpheus have primarily relied on the examination of morphological traits or comparative morphometric measurements, with an emphasis on variation in the major chela and rostro-orbital region. We applied an integrated approach that combines molecular genetics and geometric morphometrics to investigate the A. gracilipes Stimpson, 1860 species complex. We additionally applied geometric morphometric techniques to study the major chela and the rostrum across different species, and used three mitochondrial genes (12S, COI, and 16S) to reconstruct phylogenetic relationships of this complex. Our results demonstrate the first application of geometric morphometric techniques to Alpheus snapping shrimps, and highlight the significance of the major chela and rostrum as taxonomically informative traits. Furthermore, we use DNA barcodes and geometric morphometric techniques to the A. gracilipes species complex to reveal two previously unidentified cryptic species. We present the first phylogenetic reconstruction of this species complex, with new localities and expanded distribution ranges reported for many species.

Extensive sampling around Martinique during the Muséum National d’Histoire Naturelle ‘Madibenthos’ expedition in 2016 resulted in a collection of hundreds of alpheid shrimps, of which 21 distinct species of Synalpheus Spence Bate, 1888 are studied herein. Combining results of a morphological analysis, a phylogenetic tree (combined 16S and COI ) and species delimitation analyses (ABGD and PTP) indicates three species as new to science. These species are S. chaki sp. nov., S. corbariae sp. nov., and S. macdonaldi sp. nov. The first two new species belong to the S. rathbunae Coutière, 1909 species group, whereas the third new species broadly groups with the S. gambarelloides group. Additionally, 13 new country records of Synalpheus are reported for Martinique.

Although eusocial animals often achieve ecological dominance in the ecosystems where they occur, many populations are unstable, resulting in local extinction. Both patterns may be linked to the characteristic demography of eusocial species—high reproductive skew and reproductive division of labor support stable effective population sizes that make eusocial groups more competitive in some species, but also lower effective population sizes that increase susceptibility to population collapse in others. Here, we examine the relationship between demography and social organization in Synalpheus snapping shrimps, a group in which eusociality has evolved recently and repeatedly. We show using coalescent demographic modeling that eusocial species have had lower but more stable effective population sizes across 100,000 generations. Our results are consistent with the idea that stable population sizes may enable competitive dominance in eusocial shrimps, but they also suggest that recent population declines are likely caused by eusocial shrimps’ heightened sensitivity to environmental changes, perhaps as a result of their low effective population sizes and localized dispersal. Thus, although the unique life histories and demography of eusocial shrimps have likely contributed to their persistence and ecological dominance over evolutionary time scales, these social traits may also make them vulnerable to contemporary environmental change.