The long‐term impact of river regulation on fish functional diversity by a dam immediately upstream from the upper Paraná River floodplain, Brazil, was evaluated. It was expected that the resulting ...alterations in natural flow, downstream from the dam, would negatively impact fish species, resulting in a functional simplification of the ichthyofauna. In addition, this effect was expected to be more pronounced in the directly affected main channel of the Paraná River than in its tributaries, the Baía and Ivinhema rivers.
Fish were sampled before (pre) and after (post) dam closure (the intervention). The functional traits used were diet, habitat use, mouth position, migration, parental care, internal fertilisation and maximum total length. Differences in trait composition between periods (pre and post) were tested using a PERMANOVA main‐test. An indicator value analysis (IndVal) was applied to identify which traits significantly increased or decreased in abundance after the intervention. The indexes used were functional richness (FRic), Rao's quadratic entropy (FDQ) and functional redundancy (FRed). The intervention analysis based on linear models for time series was used to evaluate differences in these indexes over time.
Traits most representative during pre‐intervention were large‐bodied species with long reproductive migrations, pelagic, with subterminal and superior mouths, and herbivorous. Traits most representative during the post‐intervention were omnivorous species, with parental care, benthopelagic and insectivorous, which typically characterise fishes that inhabit stable environments. FRic decreased in Paraná and Baía rivers after the construction of the dam. However, the Ivinhema River showed an increase in mean FRic in the post‐intervention period. FDQ decreased substantially in all three rivers, while FRed increased.
The combined results of FRic, FDQ and FRed corroborate the functional simplification hypothesis expected from flow regulation by dams on functional diversity. As expected, the most pronounced simplification occurred in the Paraná River. Therefore, hydroelectric power plants can act as environmental filters strongly selecting functional traits of the downstream fish fauna, generating long‐lasting impacts on ecosystem functioning and services.
Landscape dynamics are widely thought to govern the tempo and mode of continental radiations, yet the effects of river network rearrangements on dispersal and lineage diversification remain poorly ...understood. We integrated an unprecedented occurrence dataset of 4,967 species with a newly compiled, time-calibrated phylogeny of South American freshwater fishes-the most species-rich continental vertebrate fauna on Earth-to track the evolutionary processes associated with hydrogeographic events over 100 Ma. Net lineage diversification was heterogeneous through time, across space, and among clades. Five abrupt shifts in net diversification rates occurred during the Paleogene and Miocene (between 30 and 7 Ma) in association with major landscape evolution events. Net diversification accelerated from the Miocene to the Recent (c. 20 to 0 Ma), with Western Amazonia having the highest rates of in situ diversification, which led to it being an important source of species dispersing to other regions. All regional biotic interchanges were associated with documented hydrogeographic events and the formation of biogeographic corridors, including the Early Miocene (c. 23 to 16 Ma) uplift of the Serra do Mar and Serra da Mantiqueira and the Late Miocene (c. 10 Ma) uplift of the Northern Andes and associated formation of the modern transcontinental Amazon River. The combination of high diversification rates and extensive biotic interchange associated with Western Amazonia yielded its extraordinary contemporary richness and phylogenetic endemism. Our results support the hypothesis that landscape dynamics, which shaped the history of drainage basin connections, strongly affected the assembly and diversification of basin-wide fish faunas.
ABSTRACT The cichlid Astronotus crassipinnis (Heckel, 1840) known as “oscar” or “apaiari” is native to the Amazon basin and presents an omnivorous feeding habit, with a tendency to carnivory. The ...species was introduced in the upper Paraná River floodplain, where the trophic strategies adopted by the species are not well-known. The objective of this study was to characterize the diet of A. crassipinnis in different size classes to identify ontogenetic differences in diet composition and to determine its feeding behavior in the invaded floodplain. In addition, we experimentally compared the feeding behavior of A. crassipinnis with Hoplias sp. 2, a native piscivorous. We evaluated the predation rate of the two species with different prey (fish and shrimp). Astronotus crassipinnis consumed items from several trophic levels in the juvenile stage, characterizing an omnivore feeding. In the adult stage, A. crassipinnis displayed a specialist strategy in which fish and mollusks dominated the diet. Under controlled conditions, A. crassipinnis consumed more shrimp than Hoplias sp. 2. The preference for shrimp during the experiment contrasted to its feeding in natural environments, showing the potential trophic plasticity of A. crassipinnis. The piscivorous habit in the invaded environment can be considered a trophic strategy of A. crassipinnis, which feeds on an abundant resource in the upper Paraná River floodplain. In conclusion, the ontogenetic diet shifts and the trophic opportunism of the carnivore adults can be the strategies used by the species to invade and settle the floodplain. The piscivorous strategy of A. crassipinnis may impact fish biodiversity, altering ecosystem functioning.
RESUMO Astronotus crassipinnis (Heckel, 1840), conhecido como “oscar” ou “apaiari”, é nativo da bacia Amazônica e apresenta hábito alimentar onívoro, com tendência à carnivoria. A espécie foi introduzida na planície de inundação do alto rio Paraná, onde as estratégias tróficas adotadas pela espécie não são bem conhecidas. O objetivo deste estudo foi caracterizar a dieta de A. crassipinis em diferentes classes de comprimento para identificar diferenças ontogenéticas na composição da dieta e determinar seu comportamento alimentar na planície de inundação invadida. Em adição, nós comparamos experimentalmente o comportamento alimentar de A. crassipinnis com Hoplias sp. 2, um piscívoro nativo. Avaliamos a taxa de predação das duas espécies com presas diferentes (peixes e camarões). Astronotus crassipinnis consumiu itens de diferentes níveis tróficos no estágio juvenil, caracterizando uma alimentação onívora. No estágio adulto, A. crassipinnis apresentou uma estratégia especialista em que peixes e moluscos dominaram a dieta. Em condições controladas, A. crassipinnis consumiu mais camarões que Hoplias sp. 2. A preferência por camarão durante o experimento em contraste com sua alimentação em ambientes naturais evidencia a alta plasticidade trófica de A. crassipinnis. O hábito piscívoro no ambiente invadido pode ser considerado uma estratégia trófica de A. crassipinnis, que se alimenta de um recurso abundante na planície do alto Rio Paraná. Em conclusão, as mudanças ontogenéticas na dieta e o oportunismo trófico dos adultos podem ser as estratégias utilizadas pela espécie para invadir e colonizar a planície de inundação. A estratégia piscívora de A. crassipinnis pode impactar a biodiversidade de peixes, alterando o funcionamento do ecossistema.
A
bstract
Prey fish species can respond to the presence of predators using a variety of antipredatory behaviors to reduce their risk of being consumed. As such behaviors may also imply fitness costs, ...the ability of prey to perceive and appropriately respond to the predation threat is crucial to determine the persistence of its populations. Little is known whether antipredatory behaviors adopted by prey fish species are predator-specific or a general strategy employed regardless of predator species. Here, we used two phylogenetically close piscivorous fish species (
Hoplias
sp. 2 and
Hoplerythrinus unitaeniatus
) with similar morphology and foraging strategy (ambushing) to test whether prey (
Moenkhausia sanctaefilomenae
and
Astyanax lacustris
) behavioral responses were related to predator species identity. We video recorded and evaluated prey refuge use, habitat segregation, shoal formation, and mobility in microcosms before and after the addition of each predator. We found that
M
.
sanctaefilomenae
responded to the addition of
Hoplias
sp. 2 by reducing its mobility and keeping as far as possible from the predator location in a vigilant state, while shoal formation was employed regardless of predator species. On the other hand,
A
.
lacustris
had a consistent response to the presence of predators with no adjustment for predator species. We conclude that antipredatory responses may vary according to predator characteristics not obviously related to their morphology and foraging behavior, such as predator activity level and habitat use.
The prenatal environment is recognized as crucial for the postnatal performance in cattle. In tropical regions, pregnant beef cows commonly experience nutritional restriction during the second half ...of the gestation period. Thus, the present study was designed to analyze the genotype by prenatal environment interaction (G × Epn) and to identify genomic regions associated with the level and response in growth and reproduction-related traits of beef cattle to changes in the prenatal environment. A reaction norm model was applied to data from two Nelore herds using the solutions of contemporary groups for birth weight as a descriptor variable of the gestational environment quality. A better gestational environment favored weights until weaning, scrotal circumference at yearling, and days to first calving of the offspring. The G × Epn was strong enough to result in heterogeneity of variance components and genetic parameters in addition to reranking of estimated breeding values and SNPs effects. Several genomic regions associated with the level of performance and specific responses of the animals to variations in the gestational environment were revealed, which harbor QTLs and can be exploited for selection purposes. Therefore, genetic evaluation models considering G × Epn and special management and nutrition care for pregnant cows are recommended.
Zika virus (ZIKV) has spread in the Americas since 2015 and the potential establishment of a sylvatic transmission cycle in the continent has been hypothesized. We evaluated vector competence of five ...sylvatic Neotropical mosquito species to two ZIKV isolates. Distinct batches of Haemagogus leucoceleanus, Sabethes albiprivus, Sabethes identicus, Aedes terrens and Aedes scapularis females were respectively orally challenged and inoculated intrathoracically with ZIKV. Orally challenged mosquitoes were refractory or exhibited low infection rates. Viral dissemination was detected only in Hg. leucocelaenus, but with very low rates. Virus was not detected in saliva of any mosquito orally challenged with ZIKV, regardless of viral isolate and incubation time. When intrathoracically injected, ZIKV disseminated in high rates in Hg. leucocelaenus, Sa. identicus and Sa. albpiprivus, but low transmission was detected in these species; very low dissemination and no transmission was detected in Ae. terrens and Ae. scapularis. Together these results suggest that genetically determined tissue barriers, especially in the midgut, play a vital role in inhibiting ZIKV for transmission in the tested sylvatic mosquito species. Thus, an independent enzootic transmission cycle for ZIKV in South America is very unlikely.
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