Javier A. Rodríguez-Robles

Phylogeography of the California mountain kingsnake, Lampropeltis zonata (Colubridae)

The phylogeography of the California mountain kingsnake, Lampropeltis zonata, was studied using mitochondrial DNA sequences from specimens belonging to the seven recognized subspecies and collected throughout the range of the species. Maximum parsimony and maximum likelihood methods identified a basal split within L. zonata that corresponds to southern and northern segments of its distribution. The southern clade is composed of populations from southern California (USA) and northern Baja California, Mexico. The northern clade is divided into two subclades, a ‘coastal’ subclade, consisting of populations from the central coast of California and the southern Sierra Nevada Mountains of eastern California, and a ‘northeastern’ subclade, mainly comprised of populations north of the San Francisco Bay and from the majority of the Sierra Nevada. We suggest that past inland seaways in southwestern California and the embayment of central California constituted barriers to gene flow that resulted in the two deepest divergences within L. zonata. Throughout its evolutionary history, the northern clade apparently has undergone instances of range contraction, isolation, differentiation, and then expansion and secondary contact. Examination of colour pattern variation in 321 living and preserved specimens indicated that the two main colour pattern characters used to define the subspecies of L. zonata are so variable that they cannot be reliably used to differentiate taxonomic units within this complex, which calls into question the recognition of seven geographical races of this snake.

A meager nectar offering by an epiphytic orchid is better than nothing

When a nectar reward is relatively low in quality and quantity, is it an effective pollinator attractant? In Puerto Rico, Comparettia falcata, a hummingbird-pollinated epiphytic orchid, produces an average one-time secretion of 3.3-4.0 μl of nectar (composed of 12.9-15.1 % sugar) per flower. In contrast, nectar sugar concentrations of other hummingbird flowers on Caribbean islands are 17-37 percent, and those of Puerto Rico visited by the C. falcata pollinator have standing crops averaging 2.0-6.2 μl and daily secretion rates of 3.1-10.6 μl. In 1989 and 1990, we monitored pollinator abundance, effective flower visitation, pollinarium removals (male success), pollinations, and fruit production (female success) at two sites in the Toro Negro Forest Reserve (...)

Antipredator Responses of Anolis cristatellus (Sauria: Polychrotidae)

responses during encounters with its natural predatory snake Alsophis portoricensis: flight, immobility, body thrashing, biting, dewlapping, tail lashing, tonguebunch, head-bobbing, lateral body compression, lateral face-off, pushups, crouching, and tail autotomy. Alsophis portoricensis subduing time of Anolis cristatellus increased linearly with time the lizard spent biting the snake. Some of the behaviors (dewlapping, head-bobbing, lateral body compression, lateral face-off, pushups, and tongue-bunch) exhibited by A. cristatellus during predation episodes are also used by these lizards during social interactions. We propose, then, that all these behaviors be considered multipurpose behaviors of A. cristatellus.

Home Ranges of Gopher Snakes (Pituophis catenifer, Colubridae) in Central California

Abstract Knowledge of the home range of an animal can provide insights for studies of behavioral interactions among individuals, and long-term monitoring of particular animals is necessary to determine whether they exhibit seasonal variation in space-use patterns. I radio-tracked four adult male Pituophis catenifer (gopher snake) in central California for 14 consecutive months to investigate spatial and seasonal movement patterns. Using the fixed kernel density estimator to produce a probability contour, the 95% home ranges of P. catenifer ranged from 0.89–1.78 ha, whereas their core areas (50% polygons), the most heavily used areas of their home ranges, ranged from 0.1–0.29 ha. Movements of male P. catenifer were similar in spring and summer and decreased in autumn and winter. The telemetered snakes were close to marshes and Eucalyptus woodlands but were routinely found in grassland areas, perhaps because this habitat type may provide abundant food resources and partial protection from predators. Despite their proximity, the estimated home ranges of males 2, 3, and 4 did not overlap. These findings, and those of a previous investigation of activity patterns of P. catenifer in eastern Nebraska, suggest that syntopic gopher snakes occupy exclusive home ranges during at least part of their active season.

Climatic stability and genetic divergence in the tropical insular lizard Anolis krugi, the Puerto Rican ‘Lagartijo Jardinero de la Montaña’

Two factors that can lead to geographic structuring in conspecific populations are barriers to dispersal and climatic stability. Populations that occur in different physiographic regions may be restricted to those areas by physical and/or ecological barriers, which may facilitate the formation of phylogeographic clades. Long‐term climatic stability can also promote genetic diversification, because new clades are more likely to evolve in areas that experience lesser climatic shifts. We conducted a phylogeographic study of the Puerto Rican lizard Anolis krugi to assess whether populations of this anole show genetic discontinuities across the species’ range, and if they do, whether these breaks coincide with the boundaries of the five physiographic regions of Puerto Rico. We also assessed whether interpopulation genetic distances in A. krugi are positively correlated with relative climatic stability in the island. Anolis krugi exhibits genetic structuring, but the phylogroups do not correspond to the physiographic regions of Puerto Rico. We used climatic reconstructions of two environmental extremes of the Quaternary period, the present conditions and those during the last glacial maximum (LGM), to quantify the degree of climatic stability between sampling locations. We documented positive correlations between genetic distances and relative climatic stability, although these associations were not significant when corrected for autocorrelation. Principal component analyses indicated the existence of climatic niche differences between some phylogeographic clades of A. krugi. The approach that we employed to assess the relationship between climatic stability and the genetic architecture of A. krugi can also be used to investigate the impact of factors such as the spatial distribution of food sources, parasites, predators or competitors on the genetic landscape of a species.

Food Habits of the Glossy Snake, Arizona elegans, with Comparisons to the Diet of Sympatric Long-nosed Snakes, Rhinocheilus lecontei

We studied the diet of the North American glossy snake, Arizona elegans, by examining stomach contents of more than 700 museum specimens, and supplemented our findings with published dietary records. Fifty percent of 107 prey were lizards and 44% were mammals; birds and snakes composed the remaining prey. Most lizard prey were diurnal, and presumably were captured when they were inactive by nocturnally wide-foraging glossy snakes. Conversely, most rodent prey were nocturnal heteromyids that we suspect were ambushed by A. elegans, thus raising the possibility that these snakes use alternative hunting tactics on different prey types. Ninety-five percent of the specimens with food contained a single item, and all 49 prey for which we determined direction of ingestion were swallowed head-first Although smaller A. elegans consumed mammals occasionally, specimens that ate mammals were significantly larger than those that fed on lizards, and glossy snakes that took birds were larger thap those that ate mammals. Larger glossy snakes ate larger prey and added birds to their diet, but they continued to eat lizards and mammals, which suggests that there is no absolute ontogenetic change in the diet of A. elegans. For any given body size, A. elegans has a longer head, and thus a larger gape than the sympatric long-nosed snake, Rhinocheilus lecontei. This difference in relative head length may explain why smaller A. elegans are capable of predation on mammals, whereas smaller R. lecontei feed almost exclusively on lizards, and may also account in part for the higher frequency of stout-bodied phrynosomatid lizards and of mammals in the diet of glossy snakes.

FEEDING ECOLOGY OF THE DESERT NIGHTSNAKE, HYPSIGLENA TORQUATA (COLUBRIDAE)

We studied the diet of the North American desert nightsnake, Hypsiglena torquata, based on the stomach contents of 397 museum specimens, field observations, and published dietary records. Based on 92 prey from throughout much of its distribution, H. torquata, feeds mainly on sceloporine lizards and squamate eggs and occasionally eats frogs, snakes, insects, and amphisbaenians. Lizards are typically swallowed head- first, whereas frogs are swallowed from the rump. Prey mass increases with snake mass and prey/predator mass ratios range from 0.03 to at least 0.50. Three genera of abundant lizards (Cnemidophorus, Coleonyx, Xantusia) are infrequently eaten, which suggests that these lizards chemosensorily avoid desert nightsnakes. Hypsiglena arose within a Neotropical clade of predominantly nocturnal, frog-eating snakes, and its occupancy of arid western North America correlates with two derived feeding traits: at least occasional ambush predation on diurnal lizards, and inclusion of squamate eggs in its diet.

An experimental study of interspecific interactions between two Puerto Rican Anolis lizards

We analyzed the impact of interspecific interactions between two ecologically and morphologically distinct Puerto Rican lizards, Anolis gundlachi and A. evermanni, in an experimental design consisting of six 20 × 20 m plots divided into three blocks, each consisting of a pair of experimental and control plots. We removed A. gundlachi from experimental plots and monitored the response of A. evermanni. The reduction in the number of A. gundlachi resulted in a significant increase in the abundance of both adult and juvenile A. evermanni. We found no evidence for a shift in structural habitat use in A. evermanni in experimental plots. Two possible mechanisms, interspecific competition and intraguild predation, could explain the increase in abundance of A. evermanni after the removal of A. gundlachi. These results make clear that interactions still occur between A. gundlachi and A. evermanni even given their morphological and ecological differences.

Venom Function in the Puerto Rican Racer, Alsophis portoricensis (Serpentes: Colubridae)

Alsophis portoricensis is an opisthomegadont, colubrid snake that normally employs the secretion of its Duvernoys gland to subdue its prey. We studied the effect of Duvernoys gland secretion of A. portoricensis on prey digestion by comparing digestion of various structures of normally ingested lizards to that of nonenvenomated lizards force fed to snakes. Faster digestion rates were recorded for the skin, forelimbs, liver, and lungs of envenomated anoles when compared to nonenvenomated lizards. Also, overall digestion of envenomated anoles was faster than that of nonenvenomated lizards.

Historical Contingency and Animal Diets: The Origins of Egg Eating in Snakes

Evolutionary changes in animal diets must often begin through the inclusion of a novel food type as a minor component of the diet. An aspect of this initial change that has rarely been studied is the relationship between the existing diet and the use of specific novel foods. We used comparative analyses to test the hypothesis that, in snakes, feeding on squamate (lizard and snake) eggs or bird eggs—items that represent evolutionarily derived and, in most cases, minor components of the diet—is associated with feeding on squamates or birds, respectively. Phylogenetic concentrated‐changes tests indicate a significant tendency for predation on eggs to arise in snake lineages characterized by feeding on the corresponding animals. These results also generally hold for analyses including only snake species that are likely to encounter eggs and are large enough to ingest them. The inferred histories of specialized egg eaters also support the hypothesis. Because snakes often use chemical cues to recognize prey, the observed phylogenetic patterns might be explained by chemical similarities between eggs and adult animals. Our results suggest broad effects of predispositions on snake diets and thus illustrate how historical contingencies can shape the ecology of organisms.