Abstract
Morphological and size dimorphism between genders of the benthopelagic shrimp Pasiphaea sivado are reported for the first time in the present work. All five pleopod protopods of females are thinner and more elongated than the male pleopod protopods, which in turn are anteriorly rounded and have robust shapes. The shape variability of the second pleopod protopods was also analysed using geometric morphometrics techniques which clearly differentiated between the thinner, elongated shape of the females and the robust shape of males. An important application of the observations of sexual dimorphism in pleopod shape in adult P. sivado is, from now on, the ability to quickly assess the gender of individuals when fisheries and population biology studies are carried out in the field unaided by a magnifying. A critical size from which the population sex ratio biases changed from female to male dominance was found in all studied western Mediterranean populations of P. sivado. This critical size different and became progressively smaller from populations in the Alboran Sea to populations in the Catalan Sea. Concerning sex ratio, no significant tendency of gender segregation was found across the bathymetric distribution range of the species, suggesting that this species does not perform differential depth distribution by gender.
Highlights
Pasiphaeid shrimps are a group of benthopelagic and pelagic species that currently comprises a total of 98 species grouped in seven genera: Alainopasiphaea (2), Eupasiphae (4), Glyphus (1), Leptochela (15), Parapasiphae (4), Pasiphaea (67), and Psathyrocaris (5) (De Grave and Fransen 2011, Komai et al 2012)
The proportion of individuals showing appendix masculina buds was very small at sizes smaller than 11-12 mm cephalothorax length (CL), when it was probably still undeveloped in a larger proportion of males, so gender could not be correctly assigned based on this character at these small sizes
Sex ratio analysis was restricted to individuals larger than 15 mm CL to ensure a higher reliability in properly assessing gender
Summary
Pasiphaeid shrimps are a group of benthopelagic and pelagic species that currently comprises a total of 98 species grouped in seven genera: Alainopasiphaea (2), Eupasiphae (4), Glyphus (1), Leptochela (15), Parapasiphae (4), Pasiphaea (67), and Psathyrocaris (5) (De Grave and Fransen 2011, Komai et al 2012). Within the genus Pasiphaea up to four morphologically-related species groups have been recognized, including the Pasiphaea sivado group, to which a total of nine species belong (Hayashi 1999, 2006) Species of this family are distributed along a wide latitudinal range, from tropical to Arctic and sub-Antarctic waters, mainly on and above continental slopes and in the open sea, including deep-sea habitats (Clarke and Holmes 1987, Gibbons et al 1994, Tavares and Cardoso 2006). They refer mainly to the European species Pasiphaea sivado and Pasiphaea multidentata (Cartes 1993, Frank 2000, Ramirez-Llodra et al 2007), and to Pacific Ocean species such as Pasiphaea japonica and Leptochela gracilis (Nanjo 2007, Oh et al 2006)
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