Simultaneous evolution of multiple dispersal components and kernel

Abstract

Global climate is changing rapidly and is accompanied by large‐scale fragmentation and destruction of habitats. Since dispersal is the first line of defense for mobile organisms to cope with such adversities in their environment, it is important to understand the causes and consequences of evolution of dispersal. Although dispersal is a complex phenomenon involving multiple dispersal‐components like propensity (tendency to leave the natal patch) and ability (to travel long distances), the relationship between these traits is not always straight‐forward, it is not clear whether these traits can evolve simultaneously or not, and how their interactions affect the overall dispersal profile. To investigate these issues, we subjected four large (n ∼ 2400) outbred populations of Drosophila melanogaster to artificial selection for increased dispersal, in a setup that mimicked increasing habitat fragmentation over 33 generations. The propensity and ability of the selected populations were significantly greater than the non‐selected controls and the difference persisted even in the absence of proximate drivers for dispersal. The dispersal kernel evolved to have significantly greater standard deviation and reduced values of skew and kurtosis, which ultimately translated into the evolution of a greater frequency of long‐distance dispersers (LDDs). We also found that although sex‐biased dispersal exists in D. melanogaster, its expression can vary depending on which dispersal component is being measured and the environmental condition under which dispersal takes place. Interestingly though, there was no difference between the two sexes in terms of dispersal evolution. We discuss possible reasons for why some of our results do not agree with previous laboratory and field studies. The rapid evolution of multiple components of dispersal and the kernel, expressed even in the absence of stress, indicates that dispersal evolution cannot be ignored while investigating eco‐evolutionary phenomena like speed of range expansion, disease spread, evolution of invasive species and destabilization of metapopulation dynamics.

Pre‐dispersal context and presence of opposite sex modulate density dependence and sex bias of dispersal

“…Drosophila melanogaster has been used extensively to study the process of dispersal under natural (Wallace 1975, Roff 1977 and laboratory conditions (Betini et al 2015, Tung et al 2018. Following an earlier protocol (Tung et al 2018), we used a two-patch 'source-path-destination' setup to study dispersal (Fig. 1).…”

Evolution of dispersal syndrome and its corresponding metabolomic changes

“…To capture this initial hyperactivity in the selected and control flies in the presence and absence of food (Tung et al 2018), we recorded the activity for the first 6 h after introducing the flies into the glass tubes. This duration was the same as what was given to the flies to disperse during the selection process.…”

“…These populations have been subjected to artificial selection for the longest duration (69 generations, ongoing) documented in the dispersal literature, using a setup that mimics increasing habitat fragmentation over generations (Tung et al 2018). The selected populations have rapidly evolved significantly greater dispersal propensity and ability (i.e., distance covered by the dispersers) and a larger fraction of long-distance dispersers (LDDs) in the population (Tung et al 2018). Here, we assayed three behavioral traits (locomotor activity, exploration, and aggression) and three life-history traits (body size, fecundity, and life-span) of the selected lines and contrasted the results with corresponding controls.…”

Mate-finding dispersal reduces local mate limitation and sex bias in dispersal

“…VB4 undergoes selection for higher dispersal every generation, while VBC4 serves as its corresponding control . As a result of this selection, VB flies have evolved a higher dispersal propensity (proportion of dispersers) and locomotor activity than the corresponding VBC flies Tung et al 2018b).…”

“…We used two-patch source-path-destination setups (sensu Mishra et al 2018a;Mishra et al 2018b;Tung et al 2018b) to study fly dispersal. A source container (100-mL conical glass flask) is connected to a 2-m long path (transparent plastic tube; inner diameter ~1 cm), the other end of which opens into a destination container (250-mL plastic bottle) ( Fig.…”