Inbreeding depression drives evolution of dispersal and polyandry

Inbreeding depression, defined as the reduction in fitness components of offspring of related individuals compared to offspring of unrelated individuals, is a widespread phenomenon and has profound demographic and evolutionary consequences. It can reduce the mean fitness of a population and increase extinction risk, and it can affect traits evolution. Inbreeding depression is widely hypothesized to be a key driver of the evolution of, among other traits, dispersal (individual movements potentially leading to spatial gene flow) and polyandry (female mating with multiple males within a single reproductive bout), as mechanisms to avoid inbreeding. In turn, both dispersal and polyandry can change the relatedness structure within and among populations, thus affecting opportunity for inbreeding and consequent evolution of inbreeding depression. However, despite this potential major shared driver, and despite the large amount of both theoretical and empirical work, evolution of dispersal and polyandry given inbreeding have been so far studied separately, and thus we still do not know whether and how dispersal and polyandry affect each other’s evolution, and how they may feed-back onto evolution of inbreeding depression itself. Here, using a genetically-explicit individual-based model, which models realistic distributions of selection and dominance coefficients of deleterious recessive mutations underpinning inbreeding depression, I show that: 1) inbreeding depression indeed drives evolution of dispersal and polyandry; 2) there is a negative feedback between dispersal evolution and polyandry evolution, which therefore evolve as alternative inbreeding avoidance strategies; 3) inbreeding depression is mainly shaped by the level of dispersal, while polyandry has a much more limited effect.

Asymmetric Isolation and the Evolution of Behaviors Influencing Dispersal: Rheotaxis of Guppies above Waterfalls

Populations that are asymmetrically isolated, such as above waterfalls, can sometimes export emigrants in a direction from which they do not receive immigrants, and thus provide an excellent opportunity to study the evolution of dispersal traits. We investigated the rheotaxis of guppies above barrier waterfalls in the Aripo and Turure rivers in Trinidad—the later having been introduced in 1957 from a below-waterfall population in another drainage. We predicted that, as a result of strong selection against downstream emigration, both of these above-waterfall populations should show strong positive rheotaxis. Matching these expectations, both populations expressed high levels of positive rheotaxis, possibly reflecting contemporary (rapid) evolution in the introduced Turure population. However, the two populations used different behaviors to achieve the same performance of strong positive rheotaxis, as has been predicted in the case of multiple potential evolutionary solutions to the same functional challenge (i.e., “many-to-one mapping”). By contrast, we did not find any difference in rheotactic behavior above versus below waterfalls on a small scale within either river, suggesting constraints on adaptive divergence on such scales.

Metastasis and the evolution of dispersal

Despite significant progress in oncology, metastasis remains the leading cause of mortality of cancer patients. Understanding the foundations of this phenomenon could help contain or even prevent it. As suggested by many ecologists and cancer biologists, metastasis could be considered through the lens of biological dispersal: the movement of cancer cells from their birth site (the primary tumour) to other habitats where they resume proliferation (metastatic sites). However, whether this model can consistently be applied to the emergence and dynamics of metastasis remains unclear. Here, we provide a broad review of various aspects of the evolution of dispersal in ecosystems. We investigate whether similar ecological and evolutionary principles can be applied to metastasis, and how these processes may shape the spatio-temporal dynamics of disseminating cancer cells. We further discuss complementary hypotheses and propose experimental approaches to test the relevance of the evolutionary ecology of dispersal in studying metastasis.