vittata exhibit the most distinct and differentiated genitalia of all Gambusia species (similar to the male gonopodium
We used analyses of covariance (ANCOVA) to correct gonopodium
length for body length, gonad weight, liver weight, testosterone, and estradiol for whole-body weight.
Mating is accomplished solely by a gonopodial thrust, in which the male approaches the female, extends his gonopodium
, and delivers sperm.
Males from these populations differ in both size-specific behavioral rates (Ptacek and Travis 1996) and size-specific morphometry, particularly in the dimensions of the dorsal fin and gonopodium
(Travis, Ptacek, and Martin, unpubl.
Within the Poeciliidae, at least three characters evolved to give rise to the present diversity within the family: (1) internal fertilization using a transformed anal fin in males, the gonopodium
, for sperm transfer, (2) livebearing, and (3) different degrees of maternal provisioning for the developing young (Constantz 1989; Reznick & Miles 1989).
Spermatozeugmata (mature sperm bundles) came out at the base of the gonopodium
and were collected by using an aspirator.
Fertilization is internal, and males show an anal modified fin with an intermittent organ ( gonopodium
Greatest depth at pelvic fin origin of females and at origin of gonopodium
We are currently investigating the effects of the potent synthetic androgen methyltestosterone (MT) and aldosterone inhibitor spironolactone (SPL) on an androgen-dependent secondary sex characteristic (gonopodium
) in female western mosquitofish, Gambusia affinis.
In the United States and New Zealand, female mosquitofish (Gambusia sp.) exposed to pulp and paper mill effluent, both in the field and in the laboratory, develop an elongated anal fin resembling the male gonopodium
Sexual maturity in males was based on the elongation of the anal fin into the gonopodium
, and was determined in accordance with the descriptions of Turner (1941).
geiseri were counted (except at Comal River) and classified as male (presence of gonopodium
; Pyke, 2005), female (presence of gravid spot; Peden, 1973), or immature (<10 mm; lack of gonopodium
and gravid spot; Haynes and Cashner, 1995) before being released.