Annual fish: developmental adaptations for an extreme environment

Abstract

Annual fish are freshwater teleosts found in South America and Africa that are exposed to an extremely variable environment. They develop and reproduce in seasonal ponds that dry during the summer eliminating the entire adult population. Remarkably, desiccation-resistant embryos survive in these dry ponds that hatch during the next rainy season when the ponds are recreated. Among vertebrates, they represent one of the most remarkable extremophiles. They share several features with other fish models; however, they exhibit unique traits related to their peculiar life cycle. Epiboly is temporally and spatially uncoupled from organogenesis, and the embryos can undergo reversible developmental arrests (diapauses). These attributes make them a useful model to study diverse topics in developmental biology using a comparative and evolutionary approach. In this article, different aspects related to annual fish biology, taxonomy and phylogenetic considerations, reproductive strategy, and developmental characteristics with special focus on arrests, are summarized. The current challenge is to document and determine the factors that generate such high diversity and unique adaptations of annual fish. To understand this complexity, interdisciplinary approaches are being employed taking into consideration evolutionary biology, ethology, reproductive strategies, regulation of developmental mechanisms, and senescence.

Insulin-like growth factor signaling regulates developmental trajectory associated with diapause in embryos of the annual killifish Austrofundulus limnaeus

“…In fact, others have suggested that the D/R process is simply an extensive prolongation of a normally very short part of teleost development (Berois et al, 2012). If this is the case, the data presented here are consistent with reduced IGF signaling playing a key role in this unique aspect of annual killifish development as well.…”

Incubation media affect the survival, pathway and time of embryo development in Neotropical annual fish Austrolebias nigrofasciatus (Rivulidae)

“…Consequently, these fish are subject to extreme changes in physical and chemical characteristics over a short period (Volcan et al, 2011). Owing to their life cycle and peculiar adaptations to survive in the ephemeral habitats, annual fishes are considered extreme organisms (Berois et al, 2012(Berois et al, , 2014. The temporary wetlands in which they live are considered among the most threatened habitats worldwide (Amezaga et al, 2002) which compromises the conservation status of the organisms that depend on them (Gibbs, 2000).…”

Conservation status of an endangered annual fish Hypsolebias antenori (Rivulidae) from Northeastern Brazil

“…The female has a predominantly light grey body, and a pale belly with several black spots (Figure 1b). Sexual dimorphism is an important characteristic in annual fishes, which suggests that sexual selection may play a key role in the differentiation, isolation, speciation and evolution of this group of fish (Berois et al, 2012).…”