Embryonic origin and genetic basis of cave associated phenotypes in the isopod crustacean Asellus aquaticus

Hafasa Mojaddidi,Meredith E Protas,Priscilla A Erickson,Franco E Fernandez

doi:10.1038/s41598-018-34405-8

Hafasa Mojaddidi, Meredith E Protas + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-34405-8

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Abstract

Characteristics common to animals living in subterranean environments include the reduction or absence of eyes, lessened pigmentation and enhanced sensory systems. How these characteristics have evolved is poorly understood for the majority of cave dwelling species. In order to understand the evolution of these changes, this study uses an invertebrate model system, the freshwater isopod crustacean, Asellus aquaticus, to examine whether adult differences between cave and surface dwelling individuals first appear during embryonic development. We hypothesized that antennal elaboration, as well as eye reduction and pigment loss, would be apparent during embryonic development. We found that differences in pigmentation, eye formation, and number of segments of antenna II were all present by the end of embryonic development. In addition, we found that cave and surface hatchlings do not significantly differ in the relative size of antenna II and the duration of embryonic development. To investigate whether the regions responsible for eye and pigment differences could be genetically linked to differences in article number, we genotyped F2 hybrids for the four previously mapped genomic regions associated with eye and pigment differences and phenotyped these F2 hybrids for antenna II article number. We found that the region previously known to be responsible for both presence versus absence of pigment and eye size also was significantly associated with article number. Future experiments will address whether pleiotropy and/or genetic linkage play a role in the evolution of cave characteristics in Asellus aquaticus.

Highlights

One goal of evolutionary biology research is to understand the genetic basis and evolutionary history of species or populations
Our hypothesis was supported in that we found that eye, pigment, and article number differences on antenna II were established by the end of embryonic development, though article number differences were at least in part caused by differences in body size
Counter our prediction, we found that the increased relative length of antennae II in the cave form was not significantly different between cave and surface individuals by the end of embryonic development

Summary

Introduction

One goal of evolutionary biology research is to understand the genetic basis and evolutionary history of species or populations. Transcriptomes of multiple cave organisms such as the cave beetle Ptomaphagus hirtus, the fish Poecilia mexicana, and the fish Sinocyclocheilus have been sequenced and analyzed[19,20,21] All of these studies have allowed for a greater understanding of cave biology and evolution. Many of these studies focus on genomic or genetic resources instead of developmental resources because very few cave animals can be cultured in the lab and, as a result, only rarely can embryonic development be examined. Advantages of this species include the ability to raise the animals in the laboratory using limited space and resources, the existence of multiple, independently evolved cave populations, and the ability to interbreed cave and surface forms[26]

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