The importance of familiarity, relatedness, and vision in social recognition in wild and laboratory populations of a selfing, hermaphroditic mangrove fish

Detection of relatedness in chemical alarm cues by a selfing vertebrate depends on population and the life stage producing the alarm cue

Aquatic prey have impressive abilities to extract information from a variety of chemical cues. For example, they can use the alarm cues released by wounded individuals during a predator attack to learn about predation risk, and they can also distinguish kin from non-kin individuals during interactions. However, it remains unclear whether animals can combine this information on predation risk with kin recognition of the particular individuals under threat. To examine how the relatedness of the individuals in alarm cue affects behaviour we used the self-fertilizing hermaphroditic mangrove rivulus (Kryptolebias marmoratus), in which lineages produce genetically identical offspring through selfing. We explored this in two populations that differ in their level of outcrossing. We measured activity before and after exposure to alarm cue made from individuals (either adults or embryos) from their own lineage or an unrelated lineage from the same population. Fish responded weakly to embryo alarm cues, but tended to reduce their activity more when the alarm cues were from an unrelated lineage compared to alarm cues from their own lineage, particularly in fish from the outcrossing population. In contrast, there was no effect of cue relatedness on the response to adult alarm cues but there was a strong population effect. Specifically, individuals from the outcrossing population tended to react more strongly to alarm cues compared to individuals from the predominantly selfing population. We discuss the potential roles of the major histocompatibility complex in cue detection, differences between adult vs embryo alarm cues in terms of concentration and information, and underlying differences among populations and genetic lineages in their production and detection of chemical cues. Whether this kin recognition offers adaptive benefits or is simply a consequence of being able to detect relatedness in living individuals would be an exciting area for future research.

Out of water in the dark: Plasticity in visual structures and function in an amphibious fish

Many fishes encounter periods of prolonged darkness within their lifetime, yet the consequences for the visual system are poorly understood. We used an amphibious fish (Kryptolebias marmoratus) that occupies dark terrestrial environments during seasonal droughts to test whether exposure to prolonged darkness diminishes visual performance owing to reduced optic tectum (OT) size and/or neurogenesis. We performed a 3-week acclimation with a 2  ×$\times $  2 factorial design, in which fish were either acclimated to a 12 h:12 h or 0 h:24 h light:dark photoperiod in water or in air. We found that water-exposed fish had poorer visual acuity when acclimated to the dark, while air-acclimated fish had poorer visual acuity regardless of photoperiod. The ability of K. marmoratus to capture aerial prey from water followed a similar trend, suggesting that good vision is important for hunting effectively. Changes in visual acuity did not result from changes in OT size, but air-acclimated fish had 37% fewer proliferating cells in the OT than water-acclimated fish. As K. marmoratus are unable to eat on land, reducing cell proliferation in the OT may serve as a mechanism to reduce maintenance costs associated with the visual system. Overall, we suggest that prolonged darkness and air exposure can impair vision in K. marmoratus, and that changes in visual performance may be mediated, in part, by OT neurogenesis. More broadly, we show that plastic changes to the visual system of fishes can have potential consequences for organismal performance and fitness.