Interpopulation variation in dispersal behavior of fat minnow Rhynchocypris oxycephalus jouyi juveniles inhabiting fragmented habitats

In many organisms, including fishes, downstream dispersal is often phenotype-dependent. Phenotype-dependent downstream dispersal can generate evolutionary pressure via spatial sorting, which non-randomly removes phenotypes enhancing downstream dispersal from upstream populations. Spatial sorting due to downstream dispersal could accumulate in fish populations in above-barrier habitats to which dispersed individuals cannot return, resulting in functional traits that reduce downstream dispersal. This evolutionary mechanism may be more important in smaller above-barrier habitats where downstream emigration occurs over shorter dispersal distances. This study observed the dispersal behavior of fat minnow Rhynchocypris oxycephalus jouyi juveniles in an experimental tank to examine whether juveniles from small above-barrier habitats show more behaviors favorable for reducing downstream dispersal than those from large above-barrier habitats. Juveniles from small above-barrier habitats avoided downstream dispersal for longer durations than those from large above-barrier habitats, but there was no difference in the frequency of ascending attempts. These results support the notion that behavioral traits of juveniles in small above-barrier populations have been refined by spatial sorting to reduce downstream dispersal. The finding that interpopulation variation in dispersal behavior occurred only for certain dispersal directions implies that the behavioral consequences of habitat fragmentation are more complex than previously assumed.

How to measure exploration: A combined estimation method

The personality axis 'exploration-avoidance' is often measured using an open field test (OFT) from which measurements such as mobility level (e.g. distance travelled) and space use (e.g. area covered) in an unknown environment are extracted. Recently developed tracking software surprisingly includes only a measure of mobility level in their output summary. Consequently, recent articles using these software programs started to ignore a measure of space use in their determination of exploration. In this short communication, we show briefly why it is important to not overlook a measure of space use, provide an easy way to calculate such a measure, with adjustable resolution, from the available position data provided by the software and a method to determine a proxy for exploration.

Does genetic differentiation underlie behavioral divergence in response to migration barriers in sticklebacks? A common garden experiment

Abstract

Water management measures in the 1970s in the Netherlands have produced a large number of “resident” populations of three-spined sticklebacks that are no longer able to migrate to the sea. This may be viewed as a replicated field experiment, allowing us to study how the resident populations are coping with human-induced barriers to migration. We have previously shown that residents are smaller, bolder, more exploratory, more active, and more aggressive and exhibited lower shoaling and lower migratory tendencies compared to their ancestral “migrant” counterparts. However, it is not clear if these differences in wild-caught residents and migrants reflect genetic differentiation, rather than different developmental conditions. To investigate this, we raised offspring of four crosses (migrant ♂ × migrant ♀, resident ♂ × resident ♀, migrant ♂ × resident ♀, resident ♂ × migrant ♀) under similar controlled conditions and tested for differences in morphology and behavior as adults. We found that lab-raised resident sticklebacks exhibited lower shoaling and migratory tendencies as compared to lab-raised migrants, retaining the differences in their wild-caught parents. This indicates genetic differentiation of these traits. For all other traits, the lab-raised sticklebacks of the various crosses did not differ significantly, suggesting that the earlier-found contrast between wild-caught fish reflects differences in their environment. Our study shows that barriers to migration can lead to rapid differentiation in behavioral tendencies over contemporary timescales (~ 50 generations) and that part of these differences reflects genetic differentiation.

Significance statement

Many organisms face changes to their habitats due to human activities. Much research is therefore dedicated to the question whether and how organisms are able to adapt to novel conditions. We address this question in three-spined sticklebacks, where water management measures cut off some populations, prohibiting their seasonal migration to the North Sea. In a previous study, we showed that wild-caught “resident” fish exhibited markedly different behavior than migrants. To disentangle whether these differences reflect genetic differentiation or differences in the conditions under which the wild-caught fish grew up, we conducted crosses, raising the F1 offspring under identical conditions. As their wild-caught parents, the F1 of resident × resident crosses exhibited lower migratory and shoaling tendencies than the F1 of migrant × migrant crosses, while the F1 of hybrid crosses were intermediate. This suggests that ~ 50 years of isolation are sufficient to induce behaviorally relevant genetic differentiation.