Three invasive species occurring in the diets of fishes in a Neotropical floodplain

Developmental plasticity reveals hidden fish phenotypes and enables morphospace diversification

The establishment of a given phenotype is only one expression from a range of hidden developmental possibilities. Developmental plasticity at hidden reaction norms might elicit phenotypic diversification under new developmental environments. Current discussion benefits from empirical analyses that integrate multiple environmental stimuli to evaluate how plastic responses may shape phenotypic variation. We raised Megaleporinus macrocephalus fish in different environmental settings to address contributions of developmental plasticity for emergence of new phenotypes and subsequent morphospace diversification. Plastic morphotypes were evaluated at two complementary scales, the M. macrocephalus morphospace and the higher taxonomic level of Anostomidae family. Morphospace analyses demonstrated that developmental plasticity quickly releases distinct head morphotypes that were hidden in the parental monomorphic population. Plastic morphotypes occupied discrete and previously unfilled morphospace regions, a result obtained from comparisons with a control population and in analyses including several Anostomidae species. Plastic responses involved adjustments in shape and relative position of head bonesets, and fish raised under specific environmental combinations rescued phenotypic patterns described for different genera. Therefore, developmental plasticity possibly contributes to adaptive radiation in Anostomidae. Results illustrate how plastic responses enable morphospace diversification and contribute to evolution.

Influence of host diet and phylogeny on parasite sharing by fish in a diverse tropical floodplain

The patterns of parasite sharing among hosts have important implications for ecosystem structure and functioning, and are influenced by several ecological and evolutionary factors associated with both hosts and parasites. Here we evaluated the influence of fish diet and phylogenetic relatedness on the pattern of infection by parasites with contrasting life history strategies in a freshwater ecosystem of key ecological importance in South America. The studied network of interactions included 52 fish species, which consumed 58 food types and were infected with 303 parasite taxa. Our results show that both diet and evolutionary history of hosts significantly explained parasite sharing; phylogenetically close fish species and/or species sharing food types tend to share more parasites. However, the effect of diet was observed only for endoparasites in contrast to ectoparasites. These results are consistent with the different life history strategies and selective pressures imposed on these groups: endoparasites are in general acquired via ingestion by their intermediate hosts, whereas ectoparasites actively seek and attach to the gills, body surface or nostrils of its sole host, thus not depending directly on its feeding habits.