Molecular phylogeny of shrimps from the genus Lysmata (Caridea: Hippolytidae): the evolutionary origins of protandric simultaneous hermaphroditism and social monogamy

Abstract

Shrimps from the genus Lysmata are known because of their wide diversity of lifestyles, mating systems, symbiotic partnerships, and conspicuous coloration. They can occur in crowds (large aggregations), in small groups, or as socially monogamous pairs. Shrimps from this genus are rare, if not unique among crustaceans, because of their unusual sexual system. To date, the sexual system of all species investigated comprises a protandric simultaneous hermaphroditism: shrimps initially mature and reproduce as males and later in life turn into functional simultaneous hermaphrodites. The evolutionary relationships of the species within the genus are unsettled. A molecular phylogeny of the group may shed light on the evolutionary origins of the peculiar sexual and social systems of these shrimps and help resolve standing taxonomic questions long overdue. Using a 647-bp alignment of the 16S rRNA mitochondrial DNA, we examined the phylogenetic relationship of 21 species of shrimps from the genus Lysmata from several biogeographical regions; the Atlantic, Pacific, and Indo-Pacific. The resulting phylogeny indicates that the genus is paraphyletic and includes the genus Exhippolysmata. The constituent species are subdivided into three well supported clades: one group exclusively composed of neotropical species; a second clade comprising the Indo-Pacific and Atlantic symbiotic fish cleaner shrimps; and a third clade including tropical and temperate species from the Atlantic and Pacific. The molecular phylogeny presented here does not support a historical contingency hypothesis, previously proposed to explain the origins of protandric simultaneous hermaphroditism within the genus. Furthermore, the present study shows that monogamous pair-living is restricted to one monophyletic group of shrimps and therefore probably evolved only once.

Shedding light on the larval genus Eretmocaris: morphological larval features of two closely related trans-isthmian Lysmata species (Decapoda: Caridea: Hippolytidae) described on the basis of laboratory cultured material

“…Despite their similarity to L. galapagensis, larvae of L. moorei lack the unique morphological feature displayed by L. galapagensis on the third pleomere. Regardless of the close phylogenetic relationship suggested by the molecular studies by Baeza et al (2009b), Baeza (2010) and Fiedler et al (2010) between the eastern PaciWc L. galapagensis and the western Atlantic L. moorei. The most evident larval character shared by the eastern PaciWc L. galapagensis and the western Atlantic L. moorei is the presence of a very long rostrum with several teeth in late zoeal stages.…”

“…In fact, small intraspeciWc variations in larval morphology induced by environmental gradients (Schubart et al 2005) will certainly be detected only by classical approaches. An additional challenge is the occurrence of co-occurring cryptic species (Rhyne and Lin 2006), which might be more common than initially assumed (Baeza et al 2009b). …”

“…The molecular phylogeny of Lysmata has been recently studied by several authors (Baeza et al 2009b;Baeza 2010;Fiedler et al 2010). Baeza et al (2009b) and Baeza (2010) presented the molecular phylogeny of the genus based on a segment of the 16S rRNA mitochondrial DNA.…”

“…Baeza et al (2009b) and Baeza (2010) presented the molecular phylogeny of the genus based on a segment of the 16S rRNA mitochondrial DNA. The tree topology obtained by Baeza (2010) recognizes three of the main subclades previously obtained by Baeza et al (2009b), partially supports the separation of species according to the development of the accessory branch of the outer antennular Xagellum into two diVerent genera or subgenera, and shows that the monophyletic clade comprised by species of Lysmata and Exhippolysmata is divided into 4 subclades: the "Tropical American Clade", the "Cleaner Clade", the "Cosmopolitan Clade", and the "Morpho-variable Clade".…”

“…Baeza et al (2009b) and Baeza (2010) presented the molecular phylogeny of the genus based on a segment of the 16S rRNA mitochondrial DNA. The tree topology obtained by Baeza (2010) recognizes three of the main subclades previously obtained by Baeza et al (2009b), partially supports the separation of species according to the development of the accessory branch of the outer antennular Xagellum into two diVerent genera or subgenera, and shows that the monophyletic clade comprised by species of Lysmata and Exhippolysmata is divided into 4 subclades: the "Tropical American Clade", the "Cleaner Clade", the "Cosmopolitan Clade", and the "Morpho-variable Clade". Fiedler et al (2010) presents the mitochondrial (16S) and the nuclear ribosomal (28S rRNA) phylogeny of the genus, which supports the historical morphological division of Lysmata into three clades, based on the morphology of the antennular accessory branch: the "Short Accessory Branch clade" or "Hippolysmata Clade", the "Long Accessory Branch clade" or "Lysmata Clade" and the "Unguiform Branch clade".…”