Biology ETDs
Publication Date
5-19-1969
Abstract
Cnemidophorus inornatus, a species composed of males and females, is closely related to Cnemidophorus neomexicanus, a parthenogenetic species. The two occur more or less sympatrically but differ in several factors which may provide either species with an advantage. Preference for different microhabitats and antagonistic behavior between the two species tend to prevent interspecific contact and interbreeding. Disruption of the habitat may destroy these isolating mechanisms and sterile hybrids may result. Adults and juveniles of both species are active from mid-April to mid-August but juveniles are more active than adults during the colder months. The reproductive cycle of males begins in late August with testicular enlargement and spermatogenesis. Maximum testicular size is attained in April and May and regression begins in late May or early June which are periods of active mating. Cyclic enlargement of epididymides and intensification of body coloration are coincidental with the testicular cycle but reciprocal to the fat body cycle. The testicular cycle of hybrid males is distinct and nearly identical to that of male C. inornatus. Females of the two species have nearly identical reproductive cycles. Follicular enlargement begins in April or May and the earliest ovulations occur about three weeks later. Eggs are laid from the first week of June until the third week of July. Perhaps 25% of the adult females produce a second clutch each reproductive season. The first hatchlings appear in the last two weeks of July and hatching continues until the first week of September. Oviducts enlarge and begin production of secretions preliminary to receiving eggs. Fat bodies reach minimum size during the reproductive season and begin enlargement shortly after. It is unlikely that egg production could occur without preliminary fat accumulation. Responses to steroid hormones are similar in the two species and are similar to responses of mammals to the same hormones. Mating coloration of males and enlargement of epididymides can be induced by treatments with androgens. These hormones have no effect on testes or ovaries but appear to cause some enlargement of oviducts. Large dosages of estrogens do not affect follicle size but cause circulatory problems and considerable enlargement of oviducts. Clutch size is the same in the two species, the mean being 2.13 eggs per female. About 20 months are required for reproductive maturity. Typical females may live two or three years as mature adults; perhaps 25% live to reproduce in a third reproductive season. The reproductive potential of an average female of either species is about six eggs. Reproductive potential is only half as great in C. inornatus as in C. neomexicanus when based on typical populations because of the absence of males in the latter species. This factor is probably mostly compensated for by decreased viability of C. neomexicanus eggs. The aggressive behavior of C. neomexicanus, its ability to exist in disturbed habitat where C. inornatus cannot exist, and its ability to exist in areas where food is scarce, give C. neomexicanus a short-term advantage over C. inornatus. The greater genetic variation characteristic of C. inornatus probably gives this species a long-term advantage.
Project Sponsors
The American Museum of Natural History (the Theodore Roosevelt Memorial Fund)
Language
English
Document Type
Dissertation
Degree Name
Biology
Level of Degree
Doctoral
Department Name
UNM Biology Department
First Committee Member (Chair)
William George Degenhardt
Second Committee Member
William Jacob Koster
Third Committee Member
Clifford Smeed Crawford
Fourth Committee Member
William Clarence Martin
Recommended Citation
Christiansen, James L.. "Reproduction in Cnemidophorus Inornatus and C. neomexicanus." (1969). https://digitalrepository.unm.edu/biol_etds/617
