Eusociality in snapping shrimps is associated with larger genomes and an accumulation of transposable elements

Despite progress uncovering the genomic underpinnings of sociality, much less is known about how social living affects the genome. In different insect lineages, for example, eusocial species show both positive and negative associations between genome size and structure, highlighting the dynamic nature of the genome. Here, we explore the relationship between sociality and genome architecture in Synalpheus snapping shrimps that exhibit multiple origins of eusociality and extreme interspecific variation in genome size. Our goal is to determine whether eusociality leads to an accumulation of repetitive elements and an increase in genome size, presumably due to reduced effective population sizes resulting from a reproductive division of labor, or whether an initial accumulation of repetitive elements leads to larger genomes and independently promotes the evolution of eusociality through adaptive evolution. Using phylogenetically informed analyses, we find that eusocial species have larger genomes with more transposable elements (TEs) and microsatellite repeats than noneusocial species. Interestingly, different TE subclasses contribute to the accumulation in different species. Phylogenetic path analysis testing alternative causal relationships between sociality and genome architecture is most consistent with the hypothesis that TEs modulate the relationship between sociality and genome architecture. Although eusociality appears to influence TE accumulation, ancestral state reconstruction suggests moderate TE abundances in ancestral species could have fueled the initial transitions to eusociality. Ultimately, we highlight a complex and dynamic relationship between genome and social evolution, demonstrating that sociality can influence the evolution of the genome, likely through changes in demography related to patterns of reproductive skew.

The effects of temperature and pH change on the snapping sound characteristic of Alpheus edwardsii

Aim: The current study undertook manipulative experiments to observe changes in snapping shrimp sound signals in relation to temperature and pH changes. Methodology: Sounds of intertidal snapping shrimp (Alpheus edwardsii) sequentially exposed to different temperature/pH treatments manipulation for a period of 2 week each, were recorded in the laboratory and analysed. The acoustic characteristics of snapping sound signal were examined to relate to the change in temperature, pH and combination of both parameters. Results: Our results showed that there was a significant reduction in the frequency of peak amplitude of snapping sound wave following a two week exposure to a combination of temperature and pH treatments. The frequency of snapping shrimp sound decreased by approximately 30% when exposed to a 2°C increase in temperature and a 0.7 unit decrease in pH, however, elevated temperature alone caused no significant effect on the peak frequency of snapping shrimp sound. Interpretation: The finding suggests that following the prediction values of temperature and pH changes due to climate change in the coming century may implicate the ambient noise at habitats where snapping shrimps dominate.

Niche-restriction and regional endemism driving facultative coevolutionary symbiosis --- Ecology and phylogeography of two new snapping shrimps associated with a gobiid fish

Using ecological, taxonomic and phylogenetic approaches, we here describe geographically isolated symbiotic relationships between a gobiid fish and two misdescribed alpheid snapping shrimps. This was discovered in the southwestern province of the Persian Gulf, more specifically, in the harsh hyperarid intertidal zone separating the coastal ecosystem from the Middle East desert. Phylogenetic results based on the 16S rRNA gene indicate the existence of two new cryptic species within the Alpheus lobidens De Haan, 1849 species complex, described and named here as Alpheus qatari n. sp. and Alpheus arabicus n. sp. Furthermore, phylogeographic results suggest resurrection of Alpheus crassimanus Heller, 1865 within the same species complex. A phylogenetic comparison of the endemic Arabic goby Cryptocentroides arabicus (Gmelin, 1789) with some of its congeners confirms its presence along both sides of the Persian Gulf. Ecologically noteworthy is the facultative symbiotic interaction between this endemic Arabic goby with the two mentioned endemic alpheid shrimps within two distinct ecosystems. Therefore, we herewith report a case of exceptional symbiosis of a littoral fish species with two potential partners, niche-restricted to shallow intertidal zones, however, with niche differentiation defined by the adaptability of each associated shrimp species. Furthermore, the presence of the goby depends on suitable sediment needed for burrowing: either gravel in the periphery of coral reefs, or mud in the periphery of mangrove ecosystems. The corresponding ecology, taxonomic status and phylogeography are discussed with respect to the recorded facultative character of the symbiotic relationship.

Eusociality Shapes Convergent Patterns of Molecular Evolution across Mitochondrial Genomes of Snapping Shrimps

Eusociality is a highly conspicuous and ecologically impactful behavioral syndrome that has evolved independently across multiple animal lineages. So far, comparative genomic analyses of advanced sociality have been mostly limited to insects. Here, we study the only clade of animals known to exhibit eusociality in the marine realm—lineages of socially diverse snapping shrimps in the genus Synalpheus. To investigate the molecular impact of sociality, we assembled the mitochondrial genomes of eight Synalpheus species that represent three independent origins of eusociality and analyzed patterns of molecular evolution in protein-coding genes. Synonymous substitution rates are lower and potential signals of relaxed purifying selection are higher in eusocial relative to noneusocial taxa. Our results suggest that mitochondrial genome evolution was shaped by eusociality-linked traits—extended generation times and reduced effective population sizes that are hallmarks of advanced animal societies. This is the first direct evidence of eusociality impacting genome evolution in marine taxa. Our results also strongly support the idea that eusociality can shape genome evolution through profound changes in life history and demography.

Sexual dimorphism of the major chela and sex ratio as indicators of the mating system in the estuarine snapping shrimp Alpheus colombiensis Wicksten, 1988 (Decapoda: Caridea: Alpheidae)

The sexual selection over traits that favor access to mating partners could promote the emergence of sexual dimorphism when the pressure is different between sexes. Monogamous species are considered to have a low degree of sexual dimorphism. The highly diverse snapping shrimps are usually regarded as monogamous, but the mating system has been studied only in few species. We aimed to provide insights into the mating system and sexual dimorphism of Alpheus colombiensisWicksten, 1988. The adult sex ratio was female biased, and solitary ovigerous females were found, suggesting a temporary mate guarding type of mating system. Our results also revealed sexual dimorphism on the snapping claw, which is larger in males than in females. The male’s snapping claw is probably under sexual selection, which can be mediated by male-male competition or female choice. We also estimated the A. colombiensis female size at maturity at 5.2 ± 0.76 mm. Our results contradict the common idea that snapping shrimps are monogamous species, and support that A. colombiensis probably have a temporary mate guarding (e.g., males can sexually interact with more than one female, in opposition to sexual monogamy). This study also sustains the growing evidence that alpheid shrimps display snapping claw sexual dimorphism.