Geckos: The Animal Answer Guide

6. Reproduction and Development

72 Chapter 6 Reproduction and Development How do geckos reproduce? Most geckos have both male and female individuals, although there are some with only females. In geckos with two sexes there may be some sort of courtship in which the geckos use various signals to identify each other as (1) members of the same species, (2) members of opposite sexes, and (3) receptive to mating. The initial signals are sent and received at some distance, by visual and auditory means. At closer range chemical signals are used and finally the geckos may touch and even lick each other. Male and female geckos usually do not differ much in size, but in some genera they may be differently colored. Typically the male approaches the female and, if she is receptive, he bites her on the neck and positions his vent or opening of the cloaca (the common opening into which waste products and gametes are released) under hers. As in all amniotes—animals with a terrestrially adapted egg, such as reptiles and mammals—fertilization is internal . Male geckos possess a pair of structures called hemipenes (singular: hemipenis) that are used to transfer sperm to the female. At rest, these are turned inside out and lie inside the base of the tail. When mating, one of the hemipenes (they generally alternate in use) is everted through the vent and inflated with blood. One side of the hemipenis has a sulcus, or groove, in it that carries the sperm. The rest of the structure is decorated with a complex and species-specific spines, lobes, and other surface features. Although not quite a “lock-and-key” mechanism, the specific structures of the hemipenis probably help to prevent mismatched matings between different species. Copulation in geckos usually lasts only a few minutes. In some geckos females can store sperm for a long period, and it is possible 73 Reproduction and Development that she may have multiple matings. Male geckos may also mate with several different females. How can you tell the sex of a gecko? Male and female geckos usually look rather similar to each other, although in some species sexual differences in color patterns occur (see “Are male and female geckos differently colored?” in chapter 3). For these species , color alone allows males and females to be distinguished. In some geckos, males are larger than females, but in others the trend is reversed. Overall the differences in size are usually relatively small. Unlike some groups of lizards, like iguanas and chameleons, male geckos do not possess elaborate ornamentation of the body, such as brightly colored dewlaps, enAs is typical in gecko copulation, the male of this Kandyan Gecko (Cnemaspis kandiana) bites the female on the nape and brings his cloaca under hers in order to transfer sperm through one of his two hemipenes. Courtesy of Anslem de Silva. The everted hemipenis of the Madagascan Ground Gecko (Paroedura picta) showing its relationship to the tail base and the cloaca. Only one hemipenis, the left or the right, is used at a time. Courtesy of Tony Gamble. 74 Geckos: The Animal Answer Guide larged crests, or “horns” on the snout. In many species the only way to determine the sex of a gecko is to examine its cloacal region. The hemipenes of the males, when withdrawn into the body, produce bulges behind the animal’s vent. Thus, the tail base, when viewed from below, is enlarged in males, but not in females. With gentle pressure on the tail base the hemipenes can be everted to confirm the sex, but this should only be done by experts, as it is also easy to hurt the gecko or cause it to lose its tail if done improperly. Males also have more well-developed cloacal spurs (also called “postcloacal tubercles”). These are raised scales or tubercles that project laterally or dorsolaterally from the sides of the tail base. Many geckos have precloacalor femoral pores, openings on the underside of the hindlimbs and groin through which a waxy glandular secretion is released. With a few exceptions, such pores occur only in males. However, females may have small dimples in the same position that can make sexing difficult, and many genera of geckos lack such pores altogether. Another way to check sex is to examine the abdomen for signs of eggs or enlarged follicles. As many geckos have weakly pigmented bellies, it is often...