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.

Dispersal syndromes (i.e. suites of phenotypic correlates of dispersal) are potentially important determinants of local adaptation in populations. Species that exhibit sexual dimorphism in their life history or behaviour may exhibit sex-specific differences in their dispersal syndromes. Unfortunately, there is little empirical evidence of sex differences in dispersal syndromes and how they respond to environmental change or dispersal evolution. We investigated these issues using two same-generation studies and a long-term (greater than 70 generations) selection experiment on laboratory populations of There was a marked difference between the dispersal syndromes of males and females, the extent of which was modulated by nutrition availability. Moreover, dispersal evolution via spatial sorting reversed the direction of interaction in one trait (desiccation resistance), while eliminating the sex difference in another trait (body size). Thus, we show that sex differences obtained through same-generation trait-associations ('ecological dispersal syndromes') are probably environment-dependent. Moreover, even under constant environments, they are not good predictors of the sex differences in 'evolutionary dispersal syndrome' (i.e. trait-associations shaped during dispersal evolution). Our findings have implications for local adaptation in the context of sex-biased dispersal and habitat-matching, as well as for the use of dispersal syndromes as a proxy of dispersal.This article is part of the theme issue 'Linking local adaptation with the evolution of sex differences'.

Density‐dependent dispersal (DDD) has been observed across taxa, and is expected to affect phenomena such as population dynamics, biological invasions, range expansions, and community assembly. However, little is known about whether the patterns of DDD are robust to changes in the environment. For example, the pre‐dispersal context could affect the physiology of organisms, which in turn could alter their DDD. Similarly, in sexually reproducing organisms, males and females might be differentially affected by the environment, with possible changes in their dispersal properties. To investigate some of these issues, we performed three independent experiments using laboratory populations of Drosophila melanogaster, which tested the effects of pre‐dispersal context, sex of the dispersers and presence of mates on DDD. A two‐patch dispersal setup was used to estimate the dispersal propensity and temporal dispersal profile of adult fruit flies. Comparing the data from two different pre‐dispersal contexts (variable and uniform pre‐dispersal adult densities), we found that longer pre‐dispersal exposure to higher densities led to stronger negative DDD in both males and females. Surprisingly, this change in DDD strength was accompanied by a switch in the direction of sex‐biased dispersal: from female‐biased dispersal at a low density to male‐biased dispersal at a high density. Moreover, we found that patterns of both density dependence and sex bias were contingent upon the interaction of males and females, as neither sex exhibited DDD in the absence of the other. Taken together, these results suggest that DDD and sex‐biased dispersal can be labile and be driven by the environmental context. Finally, we discuss the potential implications of these findings in terms of various ecological and evolutionary processes.

Dispersal is one of the strategies for organisms to deal with climate change and habitat degradation. Therefore, investigating the effects of dispersal evolution on natural populations is of considerable interest to ecologists and conservation biologists. Although it is known that dispersal itself can evolve due to selection, the behavioral, life-history and metabolic consequences of dispersal evolution are not well understood. Here, we explore these issues by subjecting four outbred laboratory populations of Drosophila melanogaster to selection for increased dispersal. The dispersal-selected populations had similar values of body size, fecundity, and longevity as the nonselected lines (controls), but evolved significantly greater locomotor activity, exploratory tendency, and aggression. Untargeted metabolomic fingerprinting through NMR spectroscopy suggested that the selected flies evolved elevated cellular respiration characterized by greater amounts of glucose, AMP, and NAD. Concurrent evolution of higher level of Octopamine and other neurotransmitters indicate a possible mechanism for the behavioral changes in the selected lines. We discuss the generalizability of our findings in the context of observations from natural populations. To the best of our knowledge, this is the first report of the evolution of metabolome due to selection for dispersal and its connection to dispersal syndrome evolution.

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-traits 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~2500) 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 Drosophila 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.peer-reviewed)

1Dispersal is one of the strategies for organisms to deal with climate change and habitat 2 degradation. Consequently, the effects of dispersal evolution on behavioural and life-history the dispersal-selected populations had significantly greater locomotor activity, exploratory 7 tendency and aggression but similar values of body size, fecundity and longevity. Untargeted 8 metabolomics using NMR spectroscopy suggested that the selected flies had elevated levels of 9 cellular respiration and octopamine, but lesser amount of fatty acids. All these observations 10 correlate well with the behavioural data. Our results document how metabolic pathways respond 11 to dispersal selection and help us to understand the consequences of dispersal evolution at the 12 sub-organismal level.

Sex‐biased dispersal (SBD) often skews the local sex ratio in a population. This can result in a shortage of mates for individuals of the less‐dispersive sex. Such mate limitation can lead to Allee effects in populations that are small or undergoing range expansion, consequently affecting their survival, growth, stability and invasion speed. Theory predicts that mate shortage can lead to either an increase or a decrease in the dispersal of the less‐dispersive sex. However, neither of these predictions have been empirically validated. To investigate how SBD‐induced mate limitation affects dispersal of the less‐dispersive sex, we used Drosophila melanogaster populations with varying dispersal propensities. To rule out any mate‐independent density effects, we examined the behavioural plasticity of dispersal in the presence of mates as well as same‐sex individuals with differential dispersal capabilities. In the presence of high‐dispersive mates, the dispersal of both male and female individuals was significantly increased. However, the magnitude of this increase was much larger in males than in females, indicating that the former shows greater mate‐finding dispersal. Moreover, the dispersal of either sex did not change when dispersing alongside high‐ or low‐dispersive individuals of the same sex. This suggested that the observed plasticity in dispersal was indeed due to mate‐finding dispersal, and not mate‐independent density effects. Strong mate‐finding dispersal can diminish the magnitude of sex bias in dispersal. This can modulate the evolutionary processes that shape range expansions and invasions, depending on the population size. In small populations, mate‐finding dispersal can ameliorate Allee effects. However, in large populations, it can dilute the effects of spatial sorting.

Running headline: Mate finding counters sex-biased dispersalData statement: Data will be deposited in Dryad if accepted. AbstractSex-biased dispersal (SBD) often skews the local sex ratio in a population. This can result in a shortage of mates for individuals of the less-dispersive sex. Such mate limitation can lead to Allee effects in populations that are small or undergoing range expansion, consequently affecting their survival, growth, stability and invasion speed. Theory predicts that mate shortage can lead to either an increase or a decrease in the dispersal of the less-dispersive sex. However, neither of these predictions have been empirically validated. To investigate how SBD-induced mate limitation affects dispersal of the less-dispersive sex, we used Drosophila melanogaster populations with varying dispersal propensities. To rule out any mate-independent density effects, we examined the behavioral plasticity of dispersal in presence of mates as well as same-sex individuals with differential dispersal capabilities. In the presence of high-dispersive mates, the dispersal of both male and female individuals was significantly increased. However, the magnitude of this increase was much larger in males than in females, indicating that the former show greater mate-finding dispersal. Moreover, the dispersal of either sex did not change when dispersing alongside high-or low-dispersive individuals of the same sex. This suggested that the observed plasticity in dispersal was indeed due to mate-finding dispersal, and not mate-independent density effects. Strong matefinding dispersal can diminish the magnitude of sex bias in dispersal. This can modulate the evolutionary processes that shape range expansions and invasions, depending on the population size. In small populations, mate-finding dispersal can ameliorate Allee effects. However, in large populations, it can dilute the effects of spatial sorting.