Ronco, F. | Search bioRxiv

bioRxiv2020

Dynamics of sex chromosome evolution in a rapid radiation of cichlid fishes

Sex is a fundamental trait that is determined, depending on the species, by different environmental and/or genetic factors, including various types of sex chromosomes. While the functioning and emergence of sex chromosomes have been explored in species scattered across the eukaryotic tree of life, little is known about tempo and mode of sex chromosome evolution in closely related species. Here, we examine the dynamics of sex chromosome evolution in an archetypical example of adaptive radiation, the cichlid fishes of African Lake Tanganyika. Through inspection of male and female genomes from 244 cichlid taxa and the analysis of transcriptomes from 66 taxa, we identify signatures of sex chromosomes in 79 taxa, involving 12 different linkage groups. We estimate that Tanganyikan cichlids have the highest rates of sex chromosome turnover and heterogamety transitions known to date. We further show that the recruitment of chromosomes as sex chromosomes is not at random and that some chromosomes have convergently emerged as sex chromosomes in cichlids, which provides empirical support to the "limited options" hypothesis of sex chromosome evolution.

evolutionary biology↗

bioRxiv2020

Structural manipulations of a shelter resource reveal underlying preference functions in a shell-dwelling cichlid fish

Many animals can modify the environments in which they live, thereby changing the selection pressures they experience. A common example of such niche-construction is the use, creation, or modification of environmental resources for use as nests or shelters. Because these resources often have correlated structural elements, it can be difficult to disentangle the relative contribution of these elements to resource choice, and the preference functions underlying niche-construction behaviour remain hidden. Here, we present an experimental paradigm that uses 3D-scanning, -modelling, and -printing to create replicas of structures that differ with respect to key structural attributes. We show that a niche-constructing, shelldwelling cichlid fish, Neolamprologus multifasciatus, has strong open-ended preference functions for exaggerated shell replicas. Fish preferred shells that were fully intact and either enlarged, lengthened, or had widened apertures. Shell intactness was the most important structural attribute, followed by shell length, then aperture width. We disentangle the relative roles of different shell attributes, which are tightly correlated in the wild, but nevertheless differentially influence shelter choice and therefore niche construction in this species. We highlight the broad utility of our approach when compared to more traditional methods (e.g. two-choice tasks) for studying animal decision-making in a range of contexts.

evolutionary biology↗