More Like this

1. Experimental transplants demonstrate shifts in predation favour evolution of aggressive behaviours in Trinidadian killifish

   https://doi.org/10.1111/1365-2435.14724  

   Korte, Meghan; Walsh, Matthew R (February 2025, Functional Ecology)

   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. 

   more » « less
2. Does the evolution of ontogenetic niche shifts favour species coexistence? An empirical test in Trinidadian streams

   https://doi.org/10.1111/1365-2656.13912  

   Anaya‐Rojas, Jaime M.; Bassar, Ronald D.; Matthews, Blake; Goldberg, Joshua F.; King, Leighton; Reznick, David; Travis, Joseph (March 2023, Journal of Animal Ecology)

   Abstract A major question in ecology is how often competing species evolve to reduce competitive interactions and facilitate coexistence. One untested route for a reduction in competitive interactions is through ontogenetic changes in the trophic niche of one or more of the interacting species. In such cases, theory predicts that two species can coexist if the weaker competitor changes its resource niche to a greater degree with increased body size than the superior competitor.We tested this prediction using stable isotopes that yield information about the trophic position (δ¹⁵N) and carbon source (δ¹³C) of two coexisting fish species: Trinidadian guppiesPoecilia reticulataand killifishRivulus hartii.We examined fish from locations representing three natural community types: (1) where killifish and guppies live with predators, (2) where killifish and guppies live without predators and (3) where killifish are the only fish species. We also examined killifish from communities in which we had introduced guppies, providing a temporal sequence of the community changes following the transition from a killifish only to a killifish–guppy community.We found that killifish, which are the weaker competitor, had a much larger ontogenetic niche shift in trophic position than guppies in the community where competition is most intense (killifish–guppy only). This result is consistent with theory for size‐structured populations, which predicts that these results should lead to stable coexistence of the two species. Comparisons with other communities containing guppies, killifish and predators and ones where killifish live by themselves revealed that these results are caused primarily by a loss of ontogenetic niche changes in guppies, even though they are the stronger competitor. Comparisons of these natural communities with communities in which guppies were translocated into sites containing only killifish showed that the experimental communities were intermediate between the natural killifish–guppy community and the killifish–guppy–predator community, suggesting contemporary evolution in these ontogenetic trophic differences.These results provide comparative evidence for ontogenetic niche shifts in contributing to species coexistence and comparative and experimental evidence for evolutionary or plastic changes in ontogenetic niche shifts following the formation of new communities. 

   more » « less
3. Natural selection favours a larger eye in response to increased competition in natural populations of a vertebrate

   https://doi.org/10.1111/1365-2435.13334  

   Beston, Shannon M.; Walsh, Matthew R.; Higham, ed., Timothy (April 2019, Functional Ecology)

   Abstract Eye size varies notably across taxa. Much work suggests that this variation is driven by contrasting ecological selective pressures. However, evaluations of the relationship between ecological factors and shifts in eye size have largely occurred at the macroevolutionary scale. Experimental tests in nature are conspicuously absent.Trinidadian killifish,Rivulus hartii, are found across fish communities that differ in predation intensity. We recently showed that increased predation is associated with the evolution of a smaller eye. Here, we test how divergent predatory regimes alter the trajectory of eye size evolution using comparative mark–recapture experiments in multiple streams.We found that increases in eye size are associated with enhanced survival, irrespective of predation intensity. More importantly, eye size is associated with enhanced growth in communities that lack predators, while this trend is absent when predators are present.Such results argue that increased competition for food in sites that lack predators is the key driver of eye size evolution. Aplain language summaryis available for this article. 

   more » « less
4. Association Between Reduced Upstream Riparian Forest Cover and Impaired Development of Embryos From Eastern Hellbenders ( Cryptobranchus alleganiensis )

   https://doi.org/10.1111/fwb.14368  

   Funkhouser, Holly A; Case, Brian F; Groffen, Jordy; Holloway, Austin; Hopkins, William A (January 2025, Freshwater Biology)

   ABSTRACT Populations of the Eastern Hellbender, (a large‐bodied, fully aquatic salamander) inhabiting stream reaches with low catchment‐wide riparian forest cover upstream, have experienced population declines and a shift toward a geriatric population age structure. These population declines and demographic shifts might be attributed to reduced embryo viability. Reduced egg quality/viability could negatively affect recruitment and has also been known to trigger filial cannibalism in other species. Therefore, we hypothesized that in comparison to high forest cover sites, hellbender eggs collected from low forest cover sites would have a greater incidence of developmental abnormalities and lower overall viability, and that this would predict whole‐clutch cannibalism by the attending male.We collected a subset of eggs (~20–35) from 99 clutches across sites with variable upstream riparian forest cover and reared these eggs through hatching in stream water under controlled laboratory conditions. At the same time, we monitored the fate of the remaining eggs from the same clutches in the field to document the frequency of whole‐clutch filial cannibalism.We found that eggs collected from sites with lower upstream forest cover had significantly shorter embryonic development times and produced a lower percentage of viable hatchlings (hatchlings with normal development times and morphology). The average modelled viability of hatchlings was 70% higher in sites with the highest forest cover compared to our sites with the lowest forest cover. In contrast to our predictions, we did not find evidence to suggest that egg viability in the lab predicted whole‐clutch cannibalism in the field.Although forest cover was a significant predictor of egg viability and underdevelopment, substantial variance in embryonic developmental traits was unaccounted for in our models suggesting that traits associated with adults (e.g., egg and/or sperm quality) may also play a role in determining developmental outcomes. Further experiments are needed to identify what factors (e.g., egg quality, water quality) disrupt the embryonic development of hellbenders as well as the proximate stimulus that causes adult male hellbenders to eat their young.Our results emphasise the importance of restoring and protecting riparian forest cover to conserve sensitive stream species. 

   more » « less
5. Simultaneous warming and acidification limit population fitness and reveal phenotype costs for a marine copepod

   https://doi.org/10.1098/rspb.2023.1033  

   deMayo, James A; Brennan, Reid S; Pespeni, Melissa H; Finiguerra, Michael; Norton, Lydia; Park, Gihong; Baumann, Hannes; Dam, Hans G (September 2023, Proceedings of the Royal Society B: Biological Sciences)

   Phenotypic plasticity and evolutionary adaptation allow populations to cope with global change, but limits and costs to adaptation under multiple stressors are insufficiently understood. We reared a foundational copepod species,Acartia hudsonica, under ambient (AM), ocean warming (OW), ocean acidification (OA), and combined ocean warming and acidification (OWA) conditions for 11 generations (approx. 1 year) and measured population fitness (net reproductive rate) derived from six life-history traits (egg production, hatching success, survival, development time, body size and sex ratio). Copepods under OW and OWA exhibited an initial approximately 40% fitness decline relative to AM, but fully recovered within four generations, consistent with an adaptive response and demonstrating synergy between stressors. At generation 11, however, fitness was approximately 24% lower for OWA compared with the AM lineage, consistent with the cost of producing OWA-adapted phenotypes. Fitness of the OWA lineage was not affected by reversal to AM or low food environments, indicating sustained phenotypic plasticity. These results mimic those of a congener,Acartia tonsa, while additionally suggesting that synergistic effects of simultaneous stressors exert costs that limit fitness recovery but can sustain plasticity. Thus, even when closely related species experience similar stressors, species-specific costs shape their unique adaptive responses. 

   more » « less