A new sexually dichromatic miniature Hyphessobrycon (Teleostei: Characiformes: Characidae) from the Rio Formiga, upper Rio Juruena basin, Mato Grosso, Brazil, with a review of sexual dichromatism in Characiformes

Abstract

Hyphessobrycon myrmex sp. nov., is described from the Rio Formiga, upper Rio Juruena, upper Rio Tapajós basin, Mato Grosso, Brazil. The new species can be distinguished from congeners by having the lower half of the body deeply pigmented with dark chromatophores, chromatophores concentrated above the anal fin and forming a broad, diffuse, dark midlateral stripe and by having a dense concentration of dark chromatophores along unbranched dorsal-fin rays and distal portions of the two or three subsequent branched rays. In life, H. myrmex exhibits a conspicuous sexual dichromatism, with adult males red to orange and females and immatures pale yellow. A list containing 108 sexually dichromatic taxa in six families of Characiformes is provided and the distribution of this poorly known type of dimorphism across the Characiformes is discussed.

On a remarkable sexual dimorphic trait in the Characiformes related to the olfactory organ and description of a new miniature species of Tyttobrycon Géry (Characiformes: Characidae)

“…Among fishes, sexual selection is responsible for the evolution of impressive morphological novelties. Specifically in the Characiformes, secondary sexual dimorphism is commonly associated to the occurrence of bony hooks on fins, breeding tubercles, gill glands, modified scales [2–10], shape and length of the dorsal, pelvic and anal fins [11–21], and sexual dichromatism [22,23].…”

Geographic variation of Moenkhausia bonita (Characiformes: Characidae) in the rio de la Plata basin, with distributional comments on M. intermedia

“…5: orangish or reddish in male vs. pale yellowish in female), were not reported in the original description (Benine et al, 2004). This color variation, which is known as sexual dichromatism and often appears only during reproductive seasons, is present in many species of Characidae (Pastana et al, 2017).…”

New remarkable sexually dimorphic miniature species of Hyphessobrycon (Characiformes: Characidae) from the upper Rio Tapajós basin

“…Pastana et al . () studied the sexual dichromatism in Characiformes and compiled a list of representatives with this type of secondary sexual feature. The greatest diversity of dichromatic characiforms is found in Characidae, mainly in Hyphessobrycon , which comprises almost one‐third of the cases in the family (Pastana et al, ).…”

“…Secondary sexual characters are particularly important in competition for a mating partner and typically appear when individuals reach reproductive maturity (Crook, ). Colour patterns of fishes vary in their temporal expression and can be classified in two types: permanent or temporary sexual dichromatism (Kodric‐Brown, ; Pastana et al, ). The former develops at maturity and is retained for life whereas the latter refers to seasonal or ephemeral colour changes, only appearing in specific periods or situations (Kodric‐Brown, ).…”

“…The new species is herein described in the genus Hyphessobrycon following the original definition proposed by Durbin (in Eigenmann, ) and the traditional classification system of Eigenmann (), which is defined by the following combination of non‐exclusive features: lateral line incomplete, caudal fin naked, adipose fin present, premaxillary teeth in two series, inner series with five teeth and few maxillary teeth. Hyphessobrycon is one of the most species‐rich and widespread genera of the family Characidae, with more than 140 valid species, including many recently described species, distributed from southern Mexico to Río de La Plata in Argentina (Dagosta et al, ; Eschmeyer et al, ; Pastana et al, ).…”