Abstract
A great diversity of animal species adapted to life in the semi-arid Caatinga of northeastern Brazil, including seasonal killifishes, has been reported in the last three decades. More recently, field and molecular data have shown a high occurrence of cryptic species. The killifish group herein analysed, the Hypsolebiasmagnificus species complex, is endemic to the middle and southern portion of the Caatinga, occupying about 120 km along the floodplains of the middle São Francisco River and some adjacent tributaries. Species of this complex are rare and presently considered threatened with extinction, being uniquely found in pools protected by trees and bushes. Single-locus delimitation methods were used to test species limits of populations displaying different colour patterns along the whole distribution of the complex. All analyses consistently supported the three nominal species and two new, herein described: H.gardneri Costa, sp. n., from the floodplains of the middle São Francisco River and H.hamadryades Costa, sp. n., from the Gorotuba River floodplains. The phylogenetic analysis highly supports H.hamadryades as sister to a clade comprising H.gardneri and H.harmonicus. Our field observations suggest that H.hamadryades is a miniature species. This study indicates that the H.magnificus complex comprises cryptic species apparently endemic to small areas and extremely vulnerable to environmental changes, deserving high concern.
Highlights
Recent studies on the fauna of the Caatinga, a biogeographical province of northeastern Brazil, have revealed a high diversity of species adapted to survive in semi-arid conditions, including small terrestrial vertebrates (Rodrigues 2003; Nascimento et al 2013; Werneck et al 2015) and seasonal killifishes (Costa 2001; Rosa et al 2003; Costa et al 2012, 2018)
The two new species here described, H. gardneri and H. hamadryades, are respectively most similar in colour pattern to H. harmonicus and H. magnificus, what is mostly evident in the male caudal fin (Fig. 5)
In both H. gardneri and H. harmonicus, the caudal fin of males is blue-dotted on its proximal portion and has light blue bars on the distal one (Figs 2A, 5A, B), and in H. hamadryades and H. magnificus there are light blue bars scattered over the whole fin (Fig. 5C–E), contrasting with the entire blue-dotted fin in H. picturatus (Fig. 5F)
Summary
Recent studies on the fauna of the Caatinga, a biogeographical province of northeastern Brazil, have revealed a high diversity of species adapted to survive in semi-arid conditions, including small terrestrial vertebrates (Rodrigues 2003; Nascimento et al 2013; Werneck et al 2015) and seasonal killifishes (Costa 2001; Rosa et al 2003; Costa et al 2012, 2018). Hypsolebias Costa, 2006 is the most species rich and morphologically diverse seasonal killifish genus in the Caatinga, where it is represented by two clades highly supported by morphological and molecular data (Costa 2006; Costa et al 2017), the H. antenori group (Costa 2007; Costa et al 2014, 2018) and the H. magnificus group (Costa 2007) Among species of this clade is H. magnificus (Costa & Brasil, 1991) and two closely related species, H. picturatus (Costa, 2000) and H. harmonicus (Costa, 2010) (Costa 2007, 2010), which together form a species complex, called the H. magnificus complex (hereafter HMC), distinguished from all other congeners by the presence of a narrow black margin on unpaired fins and pectoral fin in males (vs black margin absent) and unpaired fins rounded or slightly pointed (vs sharply pointed) (Costa 2010). Like other closely related congeners, HMC species live only in shadowed parts of the pools, protected by dense concentration of shrubs and trees (pers. obs. 1994–2018)
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