Tom Mathies

EFFECT OF INCUBATION TEMPERATURE ON MORPHOLOGY, GROWTH, AND SURVIVAL OF JUVENILE SCELOPORUS UNDULATUS

Incubation temperature affects a wide range of phenotypic traits of hatchling rep- tiles. The main objective of this research was to determine if such phenotypic traits persist long enough in the field to have an effect on fitness. Eggs of Sceloporus undulatus lizards were incubated at six temperature regimes, five constant and one fluctuating, with means ranging from 23-33 C. Hatchlings were measured and their subsequent morphology, growth, and survival were monitored for 7-9 months, one to two months before individuals reached adult size. Phenotypic traits of lizards that hatched at the field site were used for comparative purposes. Morphological traits persisted for 7-9 mo. In contrast, growth rates did not differ among incubation temperature treatments after individuals were released in the field. Overall, 29 (27%) of 107 individuals that were released survived to the spring following hatching, and individuals from eggs incubated at the lowest tem- perature had higher survival than individuals from all other groups. The phenotypes of lizards incubated at intermediate temperatures tended to be most similar to those of field hatched lizards. We rejected two predictions about phenotypic responses to incubation temperature. The first pre- diction was that extreme incubation temperatures would be associated with the most deviant phe- notypes. Observed phenotypic responses to temperature were either linear or, only one extreme temperature produced a deviant phenotype. The second prediction was that hatchlings incubated at warm temperatures and that hatched early in the season would have higher survival in general and higher overwinter survival in particular than hatchlings incubated at cool temperatures and that hatched later in the season. The reverse was true; observed survival was greatest for hatchlings from the coolest incubation treatment that hatched last.

EXTENDED EGG RETENTION AND ITS INFLUENCE ON EMBRYONIC DEVELOPMENT AND EGG WATER BALANCE : IMPLICATIONS FOR THE EVOLUTION OF VIVIPARITY

Viviparity in squamate reptiles presumably evolves via gradual increases in the time that eggs are retained within the oviducts. We evaluated the extent and consequences of phenotypic plasticity in egg retention for the oviparous lizard Sceloporus scalaris. This species not only exhibits facultative egg retention, but has close relatives that are viviparous. Thus, S. scalaris may possess reproductive features that are transitional between oviparity and viviparity. We tested the hypothesis that oviposition normally occurs when further retention would impair embryonic development. To do so, we determined the efects of extended egg retention on embryonic development and on egg water balance for a population in which females normally retain eggs to Dufaure and Hubert stages 31.0-33.5. Under substrate conditions that inhibited oviposition, females retained eggs to stage 39.5, or 0.5 stage units short of hatching. Extending egg retention did not retard the development of embryos relative to that of embryos in control eggs. Water did not accumulate in the extraembryonic compartments of retained eggs as it did in control eggs; all water uptake was associated with the embryo. The pattern of embryonic development within retained eggs does not support the hypotheses (1) that oviposition occurs when gas exchange in utero is no longer sufficient to support the needs of the embryos, or (2) that increases in the duration of egg retention and decreases in eggshell thickness evolve concurrently. Our observations on water uptake additionally suggest that viviparity may evolve more easily in taxa that are able to preclude storage of excess water in the extraembryonic compartment of the egg while allowing retained embryos access to suficient water for normal embryonic development.

RATES OF EMBRYONIC DEVELOPMENT OF SCELOPORUS LIZARDS : DO COLD CLIMATES FAVOR THE EVOLUTION OF RAPID DEVELOPMENT?

Rapid embryonic development is a potential adaptation to cold climates. We tested this hypothesis for nine species of Sceloporus lizards from four species groups and one species of Urosaurus, an outgroup, using observations corrected for incubation temperature and hatchling size. Phylogenetically based comparisons indicated that relatively rapid development is characteristic of the scalaris species group and relatively slow development is characteristic of the undulatus species group. Comparisons within these lineages were therefore used to determine whether developmental rate was related to climate, as judged by elevation and latitude. Within the scalaris species group, developmental rates of cool climate populations of S. aeneus and S. scalaris were not faster than that of a warm climate population of S. scalaris. Within the undulatus species group, the developmental rate of cool climate populations or species were not faster than those of warm climate populations or species. In general, developmental rates of Sceloporus are lineage specific and do not appear to be adapted to local climates.

Determinants of embryonic stage at oviposition in the lizard Urosaurus ornatus.

Relatively few squamate reptiles oviposit eggs with embryos at developmental stages greater than stage 30. To investigate potential proximate and ultimate bases of this phenomenon, we experimentally induced females of the lizard Urosaurus ornatus to retain their eggs past the normal time of oviposition (NTO). This procedure allowed us to determine whether the length of egg retention is fixed or facultative and to evaluate the effects of retention on embryos, hatchlings, and females. Females were able to retain eggs facultatively for at least 29 d past the NTO. However, retention resulted in arrested development of embryos; arrest occurred at stages 30–30.5, which is only slightly more advanced than that at the NTO (stage 29.5). Embryogenesis was reinitiated when eggs were removed from females and placed in incubation media. Hatching success of these eggs was high (87%), and incubation time was not affected by the number of days that development had been arrested. However, the snout‐vent length and water content of hatchlings were negatively related to the length of retention, and they ran slower than hatchlings from control eggs obtained at the NTO. Retention of eggs past the NTO had no detectable effect on the body condition or running speeds of females. Developmental arrest and the adverse effects of retention on hatchling phenotype, if widespread among squamates, would account for the limited range of embryo stages at oviposition and act as major constraints on the evolution of viviparity.

Reproductive Biology of Male Brown Treesnakes ( Boiga irregularis ) on Guam

Abstract Reproductive biology of males in the Guam population of the Brown Treesnake, Boiga irregularis, was investigated through monthly examinations of the urogenital system organs and plasma testosterone levels. All males examined during the 12 consecutive months of the study were spermatogenic and had sperm in the ductus epididymis and ductus deferens. No evidence of testicular recrudescence or regression was observed. Testis mass did not vary among months. Epithelial height of the kidney sexual segment was the only feature examined that varied significantly among months, with lowest heights observed in May through July. Despite this variation, the sexual segment in all males was hypertrophied and contained secretory granules. Plasma testosterone levels did not vary significantly among months, were relatively low compared to those of most other snake species, and were extremely variable among individuals. There were individuals with near-zero levels in most months. Overall, the reproductive biology of males on Guam is aseasonal. In light of this finding, the claim of seasonality in the putative source population is reassessed. Testosterone levels were independent of coelomic fat body mass, which was extremely variable among males and, in many cases, quite low. Observations on morphological features suggest that individual reproductive capacity increases disproportionately with increasing body size. The possibility of facultative aseasonal/seasonal reproduction in the species is discussed. The observed capacity for continuous spermatogenesis and its relative independence from body condition may facilitate the invasive capabilities of this ecologically damaging species.

Pheromonal control of the invasive brown treesnake: potency of female sexual attractiveness pheromone varies with ovarian state.

The female sex pheromone has potential a s a control tool for the Brown Treesnake, Boiga irregularis Merrem, a pest introduced into Guam. We conducted male-guided bioassays to determine whether potency of the female pheromone varied according to reproductive state and during vitellogenesis. In weekly simultaneous choice tests, we presented males with skin lipid samples from vitellogenic females, non-vitellogenic females, conspecific males, and carrier controls. The total time each sample was tongue-flicked was recorded: mean total tongue-flick time was highest for samples from vitellogenic females followed by samples from non-vitellogenic females. Pair-wise comparisons of male tongue-flick time for samples of non-vitellogenic females versus males and vitellogenic females versus non-vitellogenic females revealed differences in some weeks, but the greatest and most frequent differences were between vitellogenic females versus males. We observed no trend in the potency of the pheromone during vitellogenesis. Pheromone potency was greatest during vitellogenesis, with lesser potency retained while non-reproductive. Efforts at chemical identification of the pheromone and development of control tools should focus on material obtained from vitellogenic females.

Overwintering Site Selection by Short-Horned Lizards (Phrynosoma hernandesi) in Northeastern Colorado

Abstract Radio telemetry was used to track 16 adult Short-Horned Lizards (Phrynosoma hernandesi) to their individual overwintering sites on the Central Plains Experimental Range (CPER) in Weld County, Colorado. Above-ground habitat characteristics of overwintering sites and randomly selected points within the study area were assessed. All individuals entered overwintering between 29 August and 19 September with a mean estimated entrance date of 7 September. Arrival of the first subzero nighttime air temperatures occurred shortly thereafter on 16 September. No lizard left its normal area of use to overwinter, and there was no tendency to aggregate. Lizards did not necessarily overwinter on warmer south-facing slopes; the proportion of overwintering sites oriented southward (0.62) was not different from random. Most lizards (75%) selected overwintering sites in the banks of washes that had relatively steep slopes and at specific locations where substrate was relatively bare and penetrable. Overwintering sites also tended to have a greater coverage of Yucca glauca (0.02%) than the general study area (0.01%). Analyses of historical soil temperature data from the CPER revealed that lizards would have to overwinter at a subsoil depth of about 1 m to avoid freezing temperatures. Banks that contain suitable hibernation sites that are located within an individuals normal area of use may be the habitat feature most important to successful overwintering.

Excluding Nontarget Species from Brown Tree Snake, Boiga irregularis (Reptilia: Colubridae), Bait Stations: Experimental Tests of Station Design and Placement

Abstract: Bait stations with toxic baits are an emerging technology for eradication of the invasive brown tree snake (Boiga irregularis) on Guam, yet potential interferences by nontarget species are largely unknown. We tested the efficacies of three bait station designs together with three commonly used station support structures to exclude nonnative rats (roof rat, Rattus rattus; Norway rat, Rattus norvegicus; Polynesian rat, Rattus exulans) and native coconut crabs (Birgus latro). When directly presented, all species readily consumed the dead neonatal mouse baits (nontoxic) including those replicating decomposing baits in the field. When bait stations were made easily accessible by placement near ground level, all rat species were able to enter all station types, but some individual roof rats and Norway rats exhibited apparent neophobia. When stations were placed up on support structures, simulating those in the field (∼1 m above ground level), numbers of station accessions by roof rats and Norway rats remained essentially unchanged, but Polynesian rats then showed almost no inclination to enter stations. However, ability to access entrances of stations (but not interiors) when on support structures was extremely high for roof rats and appreciable for the other rat species, including Polynesians. The station type currently in widest use, when placed on chain-link cyclone fence, had the highest probability of accession. Crabs readily accessed station entrances but never interiors. The two downward-angled station designs, when placed in simulated vegetation, had the lowest probabilities of accession. In areas where nontarget species are a concern, we recommend use of either of the downward-angled station designs and suspension from vegetation wherever possible.

Tools for managing invasions: acceptance of non-toxic baits by juvenile Nile monitor lizards and Burmese pythons under laboratory conditions

Nile monitor lizards (Varanus niloticus) and Burmese pythons (Python molurus bivittatus) are large, invasive, predatory reptiles, which are now well established in south Florida. Acetaminophen was recently shown to be lethal to both animals and therefore has potential for inclusion in an integrated pest management effort to control these species. However, acceptable bait matrices for both species are still needed to deliver the toxicant. We tested nine candidate bait matrices on juvenile Nile monitor lizards and Burmese pythons in the laboratory. Baits were tested fresh and also after aging at 30°C and 50% relative humidity for 24 h. Six of the nine baits were well accepted by the monitors in both fresh and aged conditions (dead neonatal mouse, dead quail chick, ground turkey, chicken liver, tilapia, and zebra finch egg). Only the fresh dead neonatal mouse and fresh dead quail chick were well accepted by the pythons. As far as we are aware, these tests are the second of such bait matrix preference tests conducted for reptiles. The implications of our results are discussed regarding further development and testing of baits in a natural setting.