Sex-determining potencies vary among female incubation temperatures in a turtle

Reptiles whose sex is determined by incubation temperature typically exhibit all-male or all-female sex ratios over a wide range of incubation temperatures. The question arises as to whether the various all-female temperatures (or the various all-male temperatures) are equivalent in their "potency", or capacity to effect female determination. In map turtles, warm incubation temperatures produce all females and cool ones produce all males. We compared sex determining potencies of two all-female temperatures, 31 degrees C and 32.5 degrees C, by incubating eggs first at a male-producing temperature (26 degrees C) and then shifting them to the warm temperatures. The resulting sex ratio was significantly more male biased in the 26 degrees C----31 degrees C shift than in the 26 degrees C----32.5 degrees C shift, indicating that 32.5 degrees C has the greater female potency. These results point to the possibility that sex determination depends on a quantitative rather than qualitative level of gene expression.     

Steroid hormone-induced male sex determination in an amniotic vertebrate.

In many reptiles, sex is determined by the temperature at which the eggs are incubated (i.e., temperature-dependent sex determination, or TSD). Past studies have shown that exogenous steroid hormones can override the effects of temperature and induce female sex determination. However, past attempts to induce male sex determination have consistently failed. In the present study, sex determination was studied in a turtle with TSD. By utilizing an incubation temperature regimen that resulted in approximately a 1:1 sex ratio in the control group, sex determination was shown to be sensitive to both exogenous androgen and estrogen treatments: androgen induced the production of male hatchlings, whereas estrogen induced the production of female hatchlings. This is the first report of an amniotic vertebrate in which an exogenous steroid hormone induces male sex determination.     

Is love in the air or at first sight? Mate finding cues used by sympatric male velvet ants (Hymenoptera: Mutillidae)

Mate finding has been examined in a wide range of hymenopteran families, with the greatest knowledge from social species and parasitoids used in pest management. Velvet ants (Hymenoptera: Mutillidae) provide a unique system to study mate finding because short‐lived flying males must find solitary, wingless females that have spatially and temporally dispersed emergence. Based on limited field observations, it is thought that male velvet ants may use visual, chemical, and vibratory cues for mate finding, though there have been no controlled experiments to test these hypotheses. Using choice experiments, this study aims to determine the role of visual and airborne chemical cues used in female detection by three sympatric species of Dasymutilla males. We find that visual cues are not used for initial female detection and that airborne chemicals are sufficient for female detection. We also discover that males readily approach females of different species, indicating airborne chemicals are not used for species recognition. Despite the lack of discrimination by males, we determined that the sympatric, morphologically similar species show no genetic introgression, and therefore some other isolating mechanism must be at play after males make initial contact with the females.     

Mating increases plasma levels of prostaglandin F2 alpha in female garter snakes

Plasma levels of prostaglandin F2 alpha (PGF2 alpha) in female red-sided garter snakes (Thamnophis sirtalis parietalis) were measured at intervals after mating or exposure to males. PGF2 alpha levels increased significantly within 15 minutes of mating and peaked 6-24 hr after mating. Females that did not mate, but received similar amounts of male courtship, had levels of PGF2 alpha significantly lower than those of females that mated. These results extend previous findings that unmated female garter snakes injected with PGF2 alpha exhibit sexual behavior characteristic of females that have mated. Together these data indicate that female garter snakes elaborate PGF2 alpha in response to stimuli associated with mating and that PGF2 alpha has a functional role in inducing post-mating declines in sexual behavior of this species.     

The relationship among ovarian condition, steroid hormones, and estrous behavior in Anolis carolinensis

The lizard Anolis carolinensis ovulates a single egg alternately from each ovary every 14 days. The ovulated egg enters the ipsilateral oviduct, acquires a shell, and is oviposited 18 or 19 days later. Thus, there is only a single egg in one of the oviducts (one-egg condition) during most of the estrous cycle, but there is a 4-5 day period when a mature, shelled egg is in one oviduct while a recently ovulated egg is in the contralateral oviduct (two-egg condition). Analysis of ovarian follicular diameters indicates that the largest follicle in a single ovary exhibits a growth spurt about halfway through its 28-day vitellogenic growth phase. The corpus luteum, once formed from the ovulated follicle, exhibits a linear decrease in weight, becoming fully regressed just before oviposition of the egg in the ipsilateral oviduct. Plasma concentrations of estradiol-17 beta and progesterone are high in two-egg animals. After oviposition, plasma concentrations of progesterone are still high in one-egg animals whereas those of estradiol-17 beta are much lower. These ovarian and hormonal changes during the estrous cycle are discussed in relation to the probable sources of estradiol-17 beta and progesterone, the control of the alternating pattern of ovulation and oviposition, and the role of steroid hormones in female sexual receptivity in this species.     

Postillumination burst of carbon dioxide in crassalacean Acid metabolism plants

Immediately following exposure to light, a postillumination burst of CO₂ has been detected in Crassulacean acid metabolism plants. A detailed study with pineapple (Ananas comosus) leaves indicates that the postillumination burst changes its amplitude and kinetics during the course of a day. In air, the postillumination burst in pineapple leaves generally is exhibited as two peaks. The postillumination burst is sensitive to atmospheric CO₂ and O₂ concentrations as well as to the light intensity under which plants are grown. We propose that the CO₂ released in the first postillumination burst peak is indicative of photorespiration since it is sensitive to either O₂ or CO₂ concentration while the second CO₂ evolution peak is likely due to decarboxylation of organic acids involved in Crassulacean acid metabolism.     

Behavioral correlates to gonadal state in the lizard, Anolis carolinensis

Female Anolis carolinensis of unknown reproductive condition were introduced into cages containing a sexually active male and the resulting sexual behavior was noted. Female sexual receptivity was found to be correlated with the stages of follicular maturation. These results suggest that sexual receptivity in female A. carolinensis is restricted to a time immediately preceding the ovulation of each follicle and is dependent upon hormonal conditions normally arising during follicular development. Evidence is offered to suggest that during the breeding season, female sexual receptivity is rhythmical and contingent upon the cyclic ovarian changes peculiar to lizards of this genus.     

A single VH gene segment encodes the immune response to phosphorylcholine: Somatic mutation is correlated with the class of the antibody

The immune response in BALB/c mice to phosphorylcholine is highly restricted in its heterogeneity. Of the 19 immunoglobulins binding phosphorylcholine for which complete V_H-segment amino acid sequences have been determined, 10 employ a single sequence, denoted T15 after the prototype V_H sequence of this group of antibodies. The remaining 9 of these V_H segments are variants differing by 1 to 8 residues from the T15 sequence. Using a cloned V_H cDNA probe complementary to the T15 sequence, we isolated from a mouse sperm genomic library clones corresponding to four V_H gene segments that by DNA sequence analysis are >85% homologous to one another. These four V_H gene segments have been denoted the T15 V_H gene family. These V_H gene segments are most, if not all, of the germline V_H gene segments that could encode the V_H sequences of antibodies that bind phosphorylcholine. One of these four genes contains the T15-V_H-coding sequence. When the T15-family V_H gene segments were compared with the complete V_H protein sequences of 19 hybridoma and myeloma immunoglobulins that bind phosphorylcholine, several striking conclusions could be drawn. First, all of these V_H regions must have arisen from the germline T15 V_H gene segment. Thus virtually the entire immune response to phosphorylcholine is derived from a single V_H-coding sequence. Nine of the 19 V_H regions were variants differing from the T15-V_H-coding sequence and, accordingly, must have arisen by a mechanism of somatic diversification. Second, the variants appear to be generated by a somatic mutation mechanism. They cannot be explained by recombination or gene conversion among members of the T15 gene family. Third, somatic mutation is correlated with the class of the antibody. All of the somatic variation is found in the V_H regions derived from antibodies of the IgA and IgG classes. The IgM molecules express the germline T15 V_H gene segment exclusively.     

The effects of progesterone on sexual behavior in male green anole lizards (Anolis carolinensis)

It is well known that androgen-dependent sexual behaviors in male mammals and birds are inhibited by exogenous progesterone (P). However, recent research on male whiptail lizards (Cnemidophorus inornatus) indicates that P can stimulate sexual and copulatory behavior. We report here both antiandrogenic and synandrogenic actions of P on sexual behavior in males of another reptile, the green anole lizard (Anolis carolinensis). Earlier reports on birds and mammals are reviewed and discussed in relation to a possible physiological role of P in influencing sexual behavior in male vertebrates.     

Hormonal independence of courtship behavior in the male garter snake

Garter snakes exhibit a dissociated reproductive tactic in which gonadal activity is minimal at the time of mating, increasing only after the breeding season has ended. Experiments are presented demonstrating that neither short-term nor longterm castration affects courtship behavior in adult male red-sided garter snakes (Thamnophis sirtalis parietalis). So long as males have passed through a low-temperature dormancy period (hibernation), castration either shortly after emergence in the spring, or before entering winter dormancy in the fall, does not prevent the display of intense courtship behavior on emergence. Similarly, males castrated during mating activity the previous spring prior to the annual testicular growth phase actively courted females on emergence from hibernation. Males adrenalectomized and castrated during low-temperature dormancy also courted females on emergence. Hypophysectomy during or before low-temperature dormancy did not prevent males from displaying high-intensity courtship behavior on emergence from hibernation. Treatment with sex steroid hormones, as well as hypothalamic and pituitary hormones, and a variety of neural and metabolic affectors also fails to elicit courtship behavior in noncourting males during the summer. It was concluded that causal mechanisms controlling courtship behavior in the red-sided garter snake are fundamentally different, at least at the physiological level, from those mechanisms described for many laboratory and domesticated species.