Biology Of Snakes Research Articles

Sexual conflict in the snake den

Red-sided garter snakes (Thamnophis sirtalis parietalis) court and mate in spring, soon after they emerge from large communal overwintering dens in south-central Manitoba. Because of a massive bias in the operational sex ratio, every female attracts intense courtship from dozens to hundreds of males. We suggest that this courtship constitutes significant ”harassment,” because it delays the females’ dispersal from the den and hence increases their vulnerability to predation. Small females may face the greatest costs, because they are less able to escape from amorous males (who court all females, even juvenile animals). Our measurements show that males are stronger and faster than females. Experimental trials confirm that the locomotor ability of females (especially small females) is greatly reduced by the weight of a courting male. Arena trials show that intense courtship stimulates females to attempt to escape. Remarkably, some females that are too small to produce offspring may nonetheless copulate. This precocious sexual receptivity may benefit juvenile females because copulation renders them unattractive to males, and thus allows them to escape more easily from the den. Female ”tactics” to escape male harassment may explain other puzzling aspects of garter snake biology including size-assortative mating, temporal patterns in dispersal from the den, avoidance of communal dens by young-of-the-year snakes, and female mimicry. Hence, sexual conflict may have influenced important features of the mating system and behavioral ecology of these animals.

Reproductive Ecology of the Horseshoe Whip Snake (Coluber hippocrepis) in the Iberian Peninsula

-Data on the reproductive ecology of the Horseshoe whip snake (Coluber hippocrepis) are scarce and largely anecdotal in northern Mediterranean populations of this species. Dissections of preserved specimens from the southeast of the Iberian Peninsula, together with field observations, provided information on size at sexual maturity, reproductive and fat body cycling, clutch size, hatching period, and feeding frequency. Males attain sexual maturity at about 500 mm snout-vent length (SVL) and females at 680 mm SVL. As with populations from Northern Africa, males exhibit a prenuptial spermatogenic cycle. The complete reproductive cycle (spermatogenesis, vitellogenesis, mating, shelling, oviposition, incubation, and hatching) occurs within the same calendar year. The northern limit of this spermatogenic cycle also coincides with the northern limit of the distribution of the species. The female reproductive cycle is seasonal, and most sexually mature females reproduce annually. Vitellogenesis is associated with a decline in the fat body level. Oviposition occurs in late June to early July, the mean clutch size is 6.8 eggs, and there is a significant correlation between female size and fecundity. Females feed rarely when gravid. The hatching period begins in late August and lasts to mid-September. Offspring size was 237 to 308 mm SVL, and offspring mass 6.1 to 9.0 g. The reproductive biology of snakes is less well understood than that of any other reptilian group except the crocodilians (Seigel and Ford, 1987). In the Western Palearctic region, most of the studies on reproductive biology of snakes have focused on viperids (Volsoe, 1944; Nilson, 1981; Saint Girons and Duguy, 1992) or colubrids from northern and central Europe (Bourliere and Petter-Rouseaux, 1955; Goodar and Spellerberg, 1980; Naulleau, 1992; Luiselli et al., 1996, 1997), and there are few studies on species inhabiting Mediterranean habitats (but see e reproductive biol gy of snakes is less ll understo d than that of any other r ptilian up except the croc dilians (Seig l and Ford, 7). In the Western Pale rcti region, most of studies on reproductive biology of snakes e focused on viperids (Vols e, 1944; Nilson, 1; Saint Girons and Dug y, 1992) or c lui s from northern and central Europe (BourCheylan et al., 1981; Hailey and Davies, 1987; Agrimi and Luiselli, 1994). Coluber hippocrepis is a long and slender-bodied colubrid, with a total length of up to 1800 mm, and no sexual dimorphism in body size (Feriche et al., 1993). It is found in a variety of warm Mediterranean habitats throughout northern Tunisia and Algeria, most regions of Morocco, and the eastern and southern half of the Iberian Peninsula. The populations inhabiting the Iberian Peninsula have been isolated from the original populations in North Africa since la et al., 1981; Hailey and Davies, 1987; i i and Luiselli, 1 94). hippocrepis is a long and slender-bodl brid, with a tota length of up to 1800 a d no sexual dimorphism in body size i e et al., 1 93). It is found in a variety of editerranean habitats throughout northisia and Algeria, most regions of Mo, a d the eastern and southern half of the i Peninsula. The populations inhabiting 202 This content downloaded from 207.46.13.83 on Sun, 23 Oct 2016 05:04:44 UTC All use subject to http://about.jstor.org/terms REPRODUCTIVE ECOLOGY OF COLUBER HIPPOCREPIS the formation of the Strait of Gibraltar, approximately 5.3 x 106 yr (Busack, 1986; B. Sanchiz, pers. cor.). Although the distribution of the species in southern Europe suggests that males should retain the spermatogenic prenuptial cycle exhibited by the specimens from Morocco (Bons, 1967; Pozuelo, 1974; Saint Girons, 1982), the reproductive biology of the populations from the northern Mediterranean Basin has not

Description of Two New Species of Coccidia (Apicomplexa: Eimeriorina) from Flat-Headed Snakes, Tantilla gracilis (Serpentes: Colubridae) and Reclassification of Misnomer Species within the Genera Isospora and Sarcocystis from Snakes

Two new species of coccidia were recovered from the feces of flat-headed snakes, Tantilla gracilis, from Texas and Arkansas, U.S.A. Oocysts of Caryospora gracilis n. sp. are spherical or subspherical, 23.7 x 22.5 (21-25 x 21-24) #m, with a thick, bilayered wall and a shape index (length/width) of 1.06 (1.00-1.12). A micropyle is absent, but an oocyst residuum and polar granule are present. Sporocysts are ovoidal, 17.1 x 12.7 (1518 x 11-13.5) ,im, with Stieda and substieda bodies. The sporocyst shape index is 1.34 (1.29-1.40). Oocysts of Isospora wilsoni n. sp. are spherical, rarely subspherical, 17.2 x 17.0 (15-19 x 14.5-19) Aim, with a thick, bilayered wall and a shape index of 1.01 (1.001.11). A micropyle, oocyst residuum, and polar granule are absent. Sporocysts are ovoidal, 10.9 x 8.4 (10.5-12 x 8-9) ,im, with Stieda and substieda bodies and a shape index of 1.30 (1.24-1.40). In addition to these new coccidia, a check-list of the coccidian genera Isospora and Sarcocystis representing species misidentified from snakes, which places most members within the genus Sarcocystis, is presented. The flat-headed snake, Tantilla gracilis, ranges from southwestern Illinois, Missouri, and eastern Kansas to southern Texas and Coahuila, Mexico (Conant & Collins, 1991). This small, secretive snake prefers rocky hillsides and is found most often in sandy soils associated with limestone. Prey include centipedes, insect larvae, and various invertebrates (Conant & Collins, 1991). Little is known of the biology of snakes in the genus Tantilla and only a few taxonomic and natural history studies have been published (see Wilson, 1982, 1983, 1987). Coccidia never have been reported from any member of the genus, but our studies revealed two undescribed species that we report below as new. MATERIALS AND METHODS Between March and August 1991, 12 flat-headed snakes were captured alive by hand from various localities in Arkansas and Texas, U.S.A. Snakes were ' We thank the Texas Parks and Wildlife Department and Arkansas Game and Fish Commission for scientific collecting permits SPR-0390-027 and 831 to C.T.M. and S.E.T., respectively. We also thank Dr. James R. Dixon for providing specimens of T. gracilis from Llano County, Texas. TRANS. AM. MICROSC. SOC., 111(1): 50-60. 1992. ? Copyright, 1992, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.112 on Wed, 29 Jun 2016 04:50:26 UTC All use subject to http://about.jstor.org/terms VOL. 111, NO. 1, JANUARY 1992

Mid-brain responses of the auditory and somatic vibration systems in snakes.

ABSTRACT Evoked slow potentials were recorded extracellularly from the mid-brains of snakes of the genus Crotalus. For the auditory and somatic systems, amplitude, latency, and duration of responses were studied as the parameters of intensity, frequency, and rise time of sinusoidal vibratory or click stimuli were varied. Recovery curves were constructed for paired stimuli and for trains. Effects of body temperature on frequency-response threshold curves were determined. Results were verified for species of the families Boidae and Colubridae. Intensity-amplitude curves increase logarithmically for c. 20 dB above threshold and then reach a plateau for the auditory system. These curves are generally increasing over a 40 dB range in the somatic system. Latency decreases monotonically with increasing intensity; it is independent of frequency for the auditory system but depends on frequency for the somatic system. Differences in shape of intensity-amplitude curves for different frequencies lead to the hypothesis that there are auditory units with different frequency-response curves. This finding is relevant to the study of the evolution of audition. Differences in intensity-amplitude curves for the somatic system and differences in latencies for different frequencies suggest that several types of somatic vibration receptors contribute to the central response. Increase in body temperature causes increase in the frequency of greatest sensitivity for the auditory system, and increases sensitivity by 1−3 dB per°C. Higher frequencies are affected more than lower frequencies. The somatic system sensitivity is increased by c. 1·5 dB per°C, except at the extremes of the frequency curve. These findings emphasize the importance of studying effects of temperature on the central nervous systems of cold-blooded vertebrates. Of relevance to the biology of snakes is the observation that snakes are not well suited, at the mid-brain level, for rapid analysis of sequential vibratory events. A principle of general biological significance supported by comparison of temporal characteristics of mid-brain responses of snakes and other animals is that latency and recovery are related to auditory specialization rather than to phylogeny.