Female Preferences for Sailfin and Body Size in the Sailfin Molly, Poecilia latipinna

Abstract

We tested the mating preference of female sailfin mollies (Poecilia latipinna) by presenting them with pairs of dummy males differing in: (I) sailfin and body size together (holding sailfin : body size ratio constant); (II) body size alone (holding sailfin size constant); (III) sailfin size alone (holding body size constant); and (IV) sailfin : body size ratio (holding total lateral projection area constant). Females spent more time near dummies of greater sailfin or greater body size. The preference functions based on the first three sets of stimuli showed a similar pattern: the preference between any two simultaneously presented dummies increased with the magnitude of the discrepancy in lateral projection area (LPA) between them. However, when LPA was held constant in expt (IV), neither body size, sailfin size, nor any particular dummy (i.e. any particular sailfin + body size combination) was preferred. These findings suggest that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. The sailfin may therefore have evolved as a way for males to exploit this sensory bias and appear larger to prospective mates.

Genetics of species differences in sailfin and shortfin mollies

“…In mollies, mating signals are composed of both behavioural features (for example, courtship displays) and morphological features (for example, enlarged dorsal fins) that enhance the attractiveness of the signal to potential mates (MacLaren et al, 2004;Kozak et al, 2008). Sailfin mollies differ from shortfin mollies in morphological traits associated with mating signals (dorsal fin size and gonopodium length) and potentially, swimming performance (caudal fin size).…”

“…However, traits associated with dorsal fin shape (length (LDF) and height (LFFR)) and caudal fin shape (depth at caudal peduncle (DCP) and length (LCF)) showed a higher percentage of additive genetic variance than other morphological traits. These fins are likely targets of sexual selection (for example, MacLaren et al, 2004;Kozak et al, 2008) Genetics of species differences in mollies SA Loveless et al sufficient additive genetic variation exists for these traits to evolve in response to selective forces (Schluter, 2001).…”

“…Variation in these traits can result in an increase or decrease in lateral projection area (the sum of body area and fin areas that encompass the lateral view of a male presented to a female during a courtship display), which has been shown to be an important target of sexual selection by female choice (Rosenthal and Evans, 1998;Karino and Matsunaga, 2002;MacLaren et al, 2004;Kozak et al, 2008). Variation in the length of the gonopodium has also been shown to exist between populations and species of poeciliid fishes (Kelly et al, 2000;Jennions and Kelly, 2002;Hankison et al, 2006), and females of one species preferred males with longer gonopodia (Langerhans et al, 2005).…”

“…These morphological traits contributed most to species differences between sailfin and shortfin mollies. Five of these morphological differences (dorsal fin characters: length of dorsal fin, length of first dorsal fin ray, number of dorsal fin rays and depth of mid-body, as well as length of the gonopodium) are likely to be influenced by sexual selection (Rosenthal and Evans, 1998;Kelly et al, 2000;Jennions and Kelly, 2002;Karino and Matsunaga, 2002;MacLaren et al, 2004;Hankison et al, 2006;Kozak et al, 2008). Four morphological differences (caudal fin characters: height and length of the caudal fin, as well as body shape characteristics: depth of caudal peduncle and pre-anal distance) are likely to be shaped by natural selection (Webb, 1982(Webb, , 1984Endler, 1995;Ghalambor et al, 2003;Langerhans et al, 2003;Hankison et al, 2006).…”

“…The dorsal fin is used as a signal in both intra-and intersexual interactions (Farr et al, 1986;Ptacek and Travis, 1996), and the exaggerated size of the dorsal fin in larger males is thought to enhance the visibility of the courtship display behaviour and make a male appear larger in size (MacLaren et al, 2004;Kozak et al, 2008). During a courtship display, males often erect the gonopodium and lower it approximately perpendicular to the body, in addition to expanding the dorsal fin (Rosen and Tucker, 1961), and such displays are also used in aggressive encounters between males (Baird, 1968;Travis, 1994).…”