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Parallel morphological evolution and habitat‐dependent sexual dimorphism in cave‐ vs. surface populations of the Asellus aquaticus (Crustacea: Isopoda: Asellidae) species complex

ABSTRACT: Abstract Studying parallel evolution (repeated, independent evolution of similar phenotypes in similar environments) is a powerful tool to understand environment‐dependent selective forces. Surface‐dwelling species that repeatedly and independently colonized caves provide unique models for such studies. The primarily surface‐dwelling Asellus aquaticus species complex is a good candidate to carry out such research, because it colonized several caves in Europe. By comparing 17 functional morphological traits between six cave and nine surface populations of the A. aquaticus species complex, we investigated population divergence in morphology and sexual dimorphism. We found habitat‐dependent population divergence in 10 out of 17 traits, likely reflecting habitat‐driven changes in selection acting on sensory systems, feeding, grooming, and antipredator mechanisms. Sexual dimorphism was present in 15 traits, explained by sexual selection acting on male traits important in male–male agonistic behavior or mate guarding and fecundity selection acting on female traits affecting offspring number and nursing. In eight traits, the degree of sexual dimorphism was habitat dependent. We conclude that cave‐related morphological changes are highly trait‐ and function‐specific and that the strength of sexual/fecundity selection strongly differs between cave and surface habitats. The considerable population variation within habitat type warrants further studies to reveal cave‐specific adaptations besides the parallel patterns. Surface‐dwelling species that repeatedly and independently colonized caves such as Asellus aquaticus provide unique models to study parallel evolution. We measured and analyzed 17 functional morphological traits on 656 individuals from 15 cave and surface populations. We found that besides the expected habitat‐related morphological changes habitat type also affected sexual dimorphism.

SUBMITTER: Balazs G

PROVIDER: S-EPMC8571603 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The freshwater isopod crustacean Asellus aquaticus has recently been developed as an emerging invertebrate cave model for studying evolutionary and developmental biology. Mostly morphological and genetic differences between cave and surface A. aquaticus populations have been described up to now, while scarce data are available on other aspects, including physiology. The purpose of this study was to advance our understanding of the physiological differences between cave A. aquaticus and its surface-dwelling counterparts. We sampled two surface populations from the surface section of the sinking Pivka River (central Slovenia, Europe), i.e. locality Pivka Polje, and locality Planina Polje, and one cave population from the subterranean section of the sinking Pivka River, i.e. locality Planina Cave. Animals were sampled in spring, summer and autumn. We measured the activities of acetylcholinesterase (AChE) and glutathione S-transferase (GST) in individuals snap-frozen in the field immediately after collection. Acetylcholinesterase is likely related to animals' locomotor activity, while GST activity is related to the metabolic activity of an organism. Our study shows significantly lower AChE and GST activities in the cave population in comparison to both surface A. aquaticus populations. This confirms the assumption that cave A. aquaticus have lower locomotor and metabolic activity than surface A. aquaticus in their respective natural environments. In surface A. aquaticus populations, seasonal fluctuations in GST activity were observed, while these were less pronounced in individuals from the more stable cave environment. On the other hand, AChE activity was generally season-independent in all populations. To our knowledge, this is the first study of its kind conducted in A. aquaticus. Our results show that among closely related cave and surface A. aquaticus populations also physiological differences are present besides the morphological and genetic. These findings contribute to a better understanding of the biology of A. aquaticus and cave crustaceans in general.

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Parallel morphological evolution and habitat‐dependent sexual dimorphism in cave‐ vs. surface populations of the Asellus aquaticus (Crustacea: Isopoda: Asellidae) species complex

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