Pnini, R. | Search bioRxiv

bioRxiv2019

Social tolerance in Octopus laqueus - a maximal entropy model

Octopus laqueus is a small tropical octopus found in Okinawa, Japan and the greater Indo-Pacific. Octopus are often viewed as solitary animals but O. laqueus live in close proximity in the wild, and will potentially encounter one another on a regular basis, raising the possibility of sociality in the species. To test for social tolerance and social repulsion in O. laqueus, animals were kept in communal tanks, and the number of dens and sex composition was varied per tank, with a set mixture of sizes and with den occupancy tracked per individual. We found that O. laqueus will socially tolerate other individuals by sharing tanks and dens, including several animals in contact and sharing a den under den-limited conditions, and with typically no loss to cannibalism or escape. However, animals also exhibit significant levels of social repulsion, and individuals often chose a solitary den when given the option. The patterns of den occupancy are observed to be consistent with a maximum entropy model. Overall, the preference to have a den is stronger than the preference to be solitary in O. laqueus, and the animals are socially tolerant of others in the tank and in a den or shelter, a first for octopuses outside mating. The relaxed disposition and social tolerance of O. laqueus make it a promising species to work with in lab, and for development into a genetic model for social behavior in octopuses.

animal behavior and cognition↗

bioRxiv2017

Experimental Evidence That Thermal Selection Shapes Mitochondrial Genome Evolution

Mitochondria are essential organelles, found within eukaryotic cells, which contain their own DNA. Mitochondrial DNA (mtDNA) has traditionally been used in population genetic and biogeographic studies as a maternally-inherited and evolutionary-neutral genetic marker. However, it is now clear that polymorphisms within the mtDNA sequence are routinely non-neutral, and furthermore several studies have suggested that such mtDNA polymorphisms are also sensitive to thermal selection. These observations led to the formulation of the \"mitochondrial climatic adaptation\" hypothesis, for which all published evidence to date is correlational. Here, we use laboratory-based experimental evolution in the fruit fly, Drosophila melanogaster, to test whether thermal selection can shift population frequencies of two mtDNA haplogroups whose natural frequencies exhibit clinal associations with latitude along the Australian east-coast. We present experimental evidence that the thermal regime in which the laboratory populations were maintained, drove changes in haplogroup frequencies across generations. Our results strengthen the emerging view that intra-specific mtDNA variants are sensitive to selection, and suggest spatial distributions of mtDNA variants in natural populations of metazoans might reflect adaptation to climatic environments rather than within-population coalescence and diffusion of selectively-neutral haplotypes across populations.\n\nImpact SummaryWe applied experimental laboratory evolution to provide the first direct test of the \"mitochondrial climatic hypothesis,\" which predicts that the variation of mitochondrial genomes across natural distributions of metazoans can be shaped by thermal selection. Our design is the first of its kind when it comes to inferring the role of thermal selection in shaping mtDNA frequencies in nature. We harness two naturally occurring mtDNA haplotypes of Drosophila melanogaster that segregate along the east coast of Australia. One of these haplotypes predominates at sub-tropical northern latitudes and the other in the temperate and cooler south of the country. We then compete these haplotypes against each other in replicated experimental fly populations submitted to one of four different thermal regimes, in either the presence or absence of infection by Wolbachia, a coevolved endosymbiont that also exhibits maternal transmission.\n\nWe confirm that when evolving in the laboratory under warmer conditions, a haplotype naturally predominating in subtropical conditions outcompetes a haplotype that predominates at cooler Australian latitudes in the wild. We see this effect on haplotype frequencies in females in populations where latent Wolbachia infections had been purged.\n\nOur results also suggest that sex-specificity of mtDNA effects, and co-occurrence of other maternally-inherited microbiotic entities - of which Wolbachia is just one example - are likely to shape the trajectories of mitochondrial genome evolution in the wild.

evolutionary biology↗