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Abstract Theory asserts larger brains facilitate behaviours that enhance fitness. Research has demonstrated that increased brain size improves cognition and survival. However, the majority of research has focused on cross‐species comparisons. Experiments that manipulate selection to investigate the connection between brain size, behaviour and fitness are needed.Trinidadian killifish (Anablepsoides hartii) live in communities with (high predation: HP) and without (killifish only: KO) predators. Predator absence is associated with high population densities, increased intraspecific competition and evolved larger brain sizes.We tested for evolutionary shifts in behaviour by subjecting second‐generation lab‐reared killifish to a mirror aggression assay. We also quantify selection on brain size and behaviour by transplanting wild HP killifish to KO sites and tracking individual fitness (growth rates) with a mark‐recapture design.Lab‐reared killifish from KO sites—specifically males—exhibited higher levels of aggression than HP killifish. In the transplant experiment, HP killifish exhibited strong increases in aggression following the introduction to KO sites. Increased brain size was correlated with increased growth in transplanted HP killifish, yet there was no association between brain size, aggression and growth.Our results indicate that declines in predation and increased competition favour increases in aggression but further research is needed to determine if and how brain size and behaviour are linked through natural selection. Read the freePlain Language Summaryfor this article on the Journal blog. 

Externally laid eggs are often responsive to environmental cues; however, it is unclear how such plasticity evolves. In Trinidad, the killifish (Anablepsoides hartii) is found in communities with and without predators. Here, killifish inhabit shallower, ephemeral habitats in sites with predators. Such shifts may increase the exposure of eggs to air and lead to possible desiccation. We compared egg-hatching plasticity between communities by rearing eggs terrestrially on peat moss or in water. The timing of hatching did not differ between communities when eggs were reared in water. Eggs from sites with predators responded to terrestrial incubation by hatching significantly earlier compared with water-reared eggs. These responses were weaker in sites with no predators. Such divergent trends show that the presence of predators is associated with evolutionary shifts in hatching plasticity. Our results provide evidence for local adaptation in embryonic plasticity at the population scale. 

ABSTRACT It has long been recognized that the environment experienced by parents can influence the traits of offspring (i.e. ‘parental effects’). Much research has explored whether mothers respond to predictable shifts in environmental signals by modifying offspring phenotypes to best match future conditions. Many organisms experience conditions that theory predicts should favor the evolution of such ‘anticipatory parental effects’, but such predictions have received limited empirical support. ‘Condition transfer effects’ are an alternative to anticipatory effects that occur when the environment experienced by parents during development influences offspring fitness. Condition transfer effects occur when parents that experience high-quality conditions produce offspring that exhibit higher fitness irrespective of the environmental conditions in the offspring generation. Condition transfer effects are not driven by external signals but are instead a byproduct of past environmental quality. They are also likely adaptive but have received far less attention than anticipatory effects. Here, we review the generality of condition transfer effects and show that they are much more widespread than is currently appreciated. Condition transfer effects are observed across taxa and are commonly associated with experimental manipulations of resource conditions experienced by parents. Our Review calls for increased research into condition transfer effects when considering the role of parental effects in ecology and evolution. 

Density-dependent selection, which promotes contrasting patterns of trait means at different population densities, has a long history in population genetics and ecology. The unifying principle from theory is that density-dependent selection operates on phenotypic traits whose values counter the effects of whatever ecological agent is limiting population growth, be it resource competition, predators, or pathogens. However, the complexity inherent in density dependence means that the same selective process can generate multiple outcomes, depending upon the details of how population density affects vital rates and the age or size structure of a population. Failure to appreciate the potential for multiple outcomes confounded many early studies of the process. Nonetheless, careful empirical work in laboratory studies, long-term field studies, and studies of sexual selection demonstrates the wide reach of density-dependent selection. The inconsistent outcomes observed in these studies call for renewed research into how the details of density dependence channel adaptive responses. 

Abstract Anthropogenic climate change has increased the frequency of drought, wildfire, and invasions of non‐native species. Although high‐severity fires linked to drought can inhibit recovery of native vegetation in forested ecosystems, it remains unclear how drought impacts the recovery of other plant communities following wildfire. We leveraged an existing rainfall manipulation experiment to test the hypothesis that reduced precipitation, fuel load, and fire severity convert plant community composition from native shrubs to invasive grasses in a Southern California coastal sage scrub system. We measured community composition before and after the 2020 Silverado wildfire in plots with three rainfall treatments. Drought reduced fuel load and vegetation cover, which reduced fire severity. Native shrubs had greater prefire cover in added water plots compared to reduced water plots. Native cover was lower and invasive cover was higher in postfire reduced water plots compared to postfire added and ambient water plots. Our results demonstrate the importance of fuel load on fire severity and plant community composition on an ecosystem scale. Management should focus on reducing fire frequency and removing invasive species to maintain the resilience of coastal sage scrub communities facing drought. In these communities, controlled burns are not recommended as they promote invasive plants. 

Abstract Invasive predatory species are frequently observed to cause evolutionary responses in prey phenotypes, which in turn may lead to evolutionary shifts in the population dynamics of prey. Research has provided a link between rates of predation and the evolution of prey population growth in the lab, but studies from natural populations are rare. Here, we tested for evolutionary changes in population dynamics parameters of zooplanktonDaphnia pulicariafollowing invasion by the predatorBythotrephes longimanusinto Lake Kegonsa, Wisconsin, US. We used a resurrection ecological approach, whereby clones from pre‐ and post‐invasive periods were hatched from eggs obtained in sediment cores and were used in a 3‐month growth experiment. Based on these data, we estimated intrinsic population growth rates (r), the shape of density dependence (θ) and carrying capacities (K) using theta‐logistic models. We found that post‐invasionDaphniamaintained a higherrandKunder these controlled, predation‐free laboratory conditions. Evidence for changes inθwas weaker. Whereas previous experimental evolution studies of predator–prey interactions have demonstrated that genotypes that have evolved under predation have inferior competitive ability when the predator is absent, this was not the case for theDaphnia. Given that our study was conducted in a laboratory environment and the possibility for genotype‐by‐environment interactions, extrapolating these apparent counterintuitive results to the wild should be done with caution. However, barring such complications, we discuss how selection for reduced predator exposure, either temporally or spatially, may have led to the observed changes. This scenario suggests that complexities in ecological interactions represents a challenge when predicting the evolutionary responses of population dynamics to changes in predation pressure in natural systems. 

It is well established that environmental signals can induce phenotypic responses that persist for multiple generations. The induction of such ‘transgenerational plasticity’ (TGP) depends upon the ability of organisms to accurately receive and process information from environmental signals. Thus, sensory systems are likely intertwined with TGP. Here we tested the link between an environmental stressor and transgenerational responses in a component of the sensory system (eye size) that is linked to enhanced vision and ecologically relevant behaviours. We reared 45 clones of Daphnia pulicaria in the presence and absence of a low-quality resource (cyanobacteria) and evaluated shifts in relative eye size in offspring. Our results revealed divergent shifts in relative eye size within- and across-generations. Parental Daphnia that were fed cyanobacteria produced a smaller eye than Daphnia fed high-quality algae. Such differences were then reversed in the offspring generation; Daphnia whose mothers were fed cyanobacteria produced larger eyes than Daphnia that were continually fed green algae. We discuss the extent to which this maternal effect on eye size is an adaptive response linked to improved foraging. 

Abstract There exists extensive variation in eye size. Much work has provided a connection between light availability and differences in eye size across taxa. Experimental tests of the role of the light environment on the evolution of eye size are lacking. Here, we performed a selection experiment that examined the influence of light availability on shifts in eye size and the connection between eye size and phototactic (anti‐predator) behaviour inDaphnia. We set‐up replicate experimental populations ofDaphnia, repeatedly evaluated phenotypic shifts in eye size during the ~50‐day experiment, and performed a common garden experiment at the end of the experiment to test for evolutionary shifts in eye size and behaviour. Our phenotypic analyses showed that eye size rapidly diverged between the light treatments; relative eye size was consistently larger in the low versus high light treatments. Selection on eye size was also modified by variation in density as increases inDaphniadensity favoured a larger eye. However, we did not observe differences in eye size between the light treatments following two generations of common garden rearing at the end of the experiment. We instead observed strong shifts in anti‐predator behaviour.Daphniafrom the low light treatment exhibited decreased phototactic responses to light. Our results show that decreased light relaxes selection on anti‐predator behaviour. Such trends provide new insights into selection on eye size and behaviour. 

The role of phenotypic plasticity in adaptive evolution has been debated for decades. This is because the strength of natural selection is dependent on the direction and magnitude of phenotypic responses to environmental signals. Therefore, the connection between plasticity and adaptation will depend on the patterns of plasticity harbored by ancestral populations before a change in the environment. Yet few studies have directly assessed ancestral variation in plasticity and tracked phenotypic changes over time. Here we resurrected historic propagules ofDaphniaspanning multiple species and lakes in Wisconsin following the invasion and proliferation of a novel predator (spiny waterflea,Bythotrephes longimanus). This approach revealed extensive genetic variation in predator-induced plasticity in ancestral populations ofDaphnia. It is unlikely that the standing patterns of plasticity shieldedDaphniafrom selection to permit long-term coexistence with a novel predator. Instead, this variation in plasticity provided the raw materials forBythotrephes-mediated selection to drive rapid shifts inDaphniabehavior and life history. Surprisingly, there was little evidence for the evolution of trait plasticity as genetic variation in plasticity was maintained in the face of a novel predator. Such results provide insight into the link between plasticity and adaptation and highlight the importance of quantifying genetic variation in plasticity when evaluating the drivers of evolutionary change in the wild.