Acetes, H. MILNE EDWARDS, 1830

Vereshchaka, Alexander L., Lunina, Anastasia A. & Olesen, Jørgen, 2016, Phylogeny and classification of the shrimp genera Acetes, Peisos, and Sicyonella (Sergestidae: Crustacea: Decapoda), Zoological Journal of the Linnean Society 177 (2), pp. 353-377 : 362-363

OF ACETES

The distributions of all recognized species of Acetes are summarized in Figure 13 . The clades A. marinus + A. paraguayensis and A. americanus + A. binghami are geographically isolated from the rest of Acetes and occur in Central, South and North America. These clades originated through allopatric divergence, whereby new species arise from geographically isolated populations of the same ancestral species. One of these clades, A. marinus + A. paraguayensis , has adapted to lowsalinity environments in South America and speciation within this clade reflects the degree of this adaptation: A. marinus lives in brackish waters, whereas A. paraguayensis is the only freshwater sergestid ( Hansen, 1919; Omori, 1975). The second American clade, A. americanus + A. binghami , occurs in the coastal waters of North, Central, and South America and shows a parapatric distribution. The two species are geographically isolated from each other by the Isthmus of Panama, which prevents gene exchange between them.

The terminal clade of Acetes occurs in the Indo- West Pacific. Speciation within this clade took place allopatrically for A. johni and A. erythraeus , which are geographically isolated from the other species of Acetes and inhabit coastal waters of the Western Indian Ocean. The rest of the species occur along a coastal line between West India and Japan and have undergone sympatric speciation. We assume that this sympatric speciation is a likely outcome of competition for resources, when the evolution of assortative mating leads to reproductive isolation between ecologically diverging subpopulations ( Dieckmann & Doebeli, 1999). Cross-breeding between sympatric species of Acetes is prevented by highly specialized copulatory structures, which differ greatly even between closely related species.

Figure 13 shows a number of blank areas from where Acetes has not yet been reported. This is probably because of a lack of sampling as the genus occurs in all well-explored coastal areas of tropical and subtropical areas. This is especially true in regard to the west coast of Africa, which contains the estuaries of big rivers such as Congo, Ebola, Gambia, Niger, Orange, and Senegal. Estuaries of these rivers would definitely be expected to harbour various species of Acetes .

Figures

Figure 13. Provisional geographical distribution of Acetes. Coloured lines indicate position of estuarine habitats for each of the known species. Semitransparent coloured areas indicate species ranges of freshwater Acetes paraguayensis and estuarine Acetes sibogae.