Biomedical subjects
R Shine
Publications and source records attributed to R Shine.
Effect of dietary calcium on blood lead concentrations in occupationally exposed and nonexposed workers.
Workers exposed to lead may benefit from a calcium-rich diet, since calcium competes with lead for intestinal absorption. We studied the effect of dietary calcium on blood lead levels. We assessed blood lead levels, dietary intake of calcium, smoking and alcohol consumption, and anthropometric and demographic data in 56 workers exposed to lead and 90 workers without such exposure. Mean intake of dietary calcium was 775 +/- 370 mg/day in the nonexposed workers and 858 +/- 423 mg/day in the exposed workers. Occupational lead exposure explained nearly 90% of the variance in blood lead levels of the entire cohort. Smoking and alcohol intake also showed significant associations with blood lead levels, but their combined effect was less than 2%. When the exposed and nonexposed workers were considered separately, no association was found between blood lead levels and calcium intake. The amount of calcium in the diet does not influence blood lead levels. Further studies are warranted to determine whether dietary calcium influences blood lead levels in exposed and nonexposed workers in other settings and in subjects with lower intakes of calcium.
Sedentary snakes and gullible geckos: predator-prey coevolution in nocturnal rock-dwelling reptiles.
We investigated (1) the importance of chemical cues for predator detection by the nocturnal, rock-dwelling velvet gecko, Oedura lesueurii, and (2) how the lizards' responses to snake odour may have exerted selection on the foraging behaviours of a nocturnal elapid snake. This snake species (broadheaded snake, Hoplocephalus bungaroides) feeds primarily on velvet geckos, and does so by means of a distinctive foraging behaviour: the snakes remain sedentary in rock crevices for days or weeks, waiting to ambush geckos. Behavioural assays showed that geckos that are sympatric with this sedentary 'ambush' predator can detect and respond to the scent of the snake. Retreat-site selection experiments showed that geckos are less likely to enter crevices if the snake's scent is distributed over the entire rock surface, rather than localized to a central portion. Together, these data support the notion that the 'ambush' predator benefits by remaining sedentary within a retreat-site for long periods, because it thereby minimizes the extent to which it spreads its scent over the rocks forming the crevice. Geckos from a population sympatric with the 'ambush' predator responded strongly to the snake scent, but those from an allopatric population did not. Additionally, geckos from sympatric populations were able to detect the scent of a nocturnal snake that does not eat geckos (small-eyed snake, Rhinoplocephalus nigrescens), but did not modify their retreat-site selection or locomotory behaviours in response to this cue. Lizards from allopatric populations apparently did not detect the scent of small-eyed snakes. Collectively, our findings support an interpretation of predator-prey coevolution in the present system, and emphasize the importance of chemosensory cues to these rock-dwelling reptiles. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.
Heat, safety or solitude? Using habitat selection experiments to identify a lizard's priorities.
Laboratory experiments with a rock-dwelling nocturnal gecko, Oedura lesueurii, showed that retreat-site selection (and other behaviours) are affected by the interplay between thermal benefits, social advantages and avoidance of predators. Velvet geckos were highly selective in habitat choice: they preferred artificial retreat-sites that mimic the thermal properties of natural rocks in full sun rather than those that mimic rocks in full shade; mature male geckos rarely shared retreat-sites with other adult males; and these lizards strongly avoided retreat-sites covered with the scent of a natural predator (the broadheaded snake, Hoplocephalus bungaroides). After documenting these preferences, we carried out additional trials in which two or more of these factors co-occurred, as is often the case in nature. Social dominance interacted with thermal benefits in determining retreat-site selection, with smaller (subordinate) males forced to use cooler retreat-sites when larger (dominant) males were present. Avoidance of predators was a higher priority than thermoregulation: the lizards would forego a warmer retreat-site with predator scent in favour of a cooler, unscented one. There was also an interplay between social dominance and predator scent: smaller males were forced to use either predator-scented retreat-sites or no retreat-site when larger males were present. General activity levels, and the frequencies of specific behavioural acts, also shifted in response to social and predator-scent cues. Our study emphasizes the complexity of habitat-selection behaviour in these lizards, and clarifies the criteria used in retreat-site selection when (as is commonly the case) the animal must choose between conflicting priorities. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.
Phylogenetic relationships between oviparous and viviparous populations of an Australian lizard (Lerista bougainvillii, scincidae).
Viviparity has evolved from oviparity in many vertebrate lineages, and species that contain both oviparous and viviparous populations offer the best opportunity for a detailed examination of the processes involved in this major life-history transition. However, although several such species have been reported, none have been the subject of detailed phylogenetic analyses. We examine such a case within the Australian scincid lizard bougainvillii. Data were obtained by sequencing a 314-bp segment of mitochondrial cytochrome b from 32 individuals from 17 populations of L. bougainvillii and two morphologically similar congeneric species (L. dorsalis L. microtus). Sequences were aligned and analyzed using parsimony and distance methods. The resultant matriarchal phylogeny resolved the populations of L. bougainvillii into three major groups: a population from NSW; a group predominantly from Eyre Peninsula; and a less well-defined group from the central part of the species range. The NSW and Eyre Peninsula groups are oviparous and are quite divergent from other L. bougainvillii populations and from each other. The central group contains both viviparous and oviparous populations, and seem to represent a more recent radiation within the species. Our results indicate that viviparity has evolved at least twice within the genus Lerista, because the viviparous L. microtus is not closely related to viviparous populations of L. bougainvillii. The lack of phylogenetic separation of mtDNAs from viviparous and oviparous populations within L. bougainvillii relative to strong geographic structure within the latter indicates that populations with different reproductive modes are indeed conspecific. Lerista bougainvillii is thus the first vertebrate species for which intraspecific bimodality in reproductive mode can be claimed with any certainty.
Phylogenetic relationships of terrestrial Australo-Papuan elapid snakes (subfamily Hydrophiinae) based on cytochrome b and 16S rRNA sequences.
Phylogenetic relationships among the venomous Australo-Papuan elapid snake radiation remain poorly resolved, despite the application of diverse data sets. To examine phylogenetic relationships among this enigmatic group, portions of the cytochrome b and 16S rRNA mitochondrial DNA genes were sequenced from 19 of the 20 terrestrial Australian genera and 6 of the 7 terrestrial Melanesian genera, plus a sea krait (Laticauda) and a true sea snake (Hydrelaps). These data clarify several significant issues in elapid phylogeny. First, Melanesian elapids form sister groups to Australian species, indicating that the ancestors of the Australian radiation came via Asia, rather than representing a relict Gondwanan radiation. Second, the two major groups of sea snakes (sea kraits and true sea snakes) represent independent invasions of the marine environment. Third, the radiation of viviparous Australian elapids is much older than has been suggested from immunological data. Parsimony analyses were unable to resolve relationships among the Australian radiation, a problem previously encountered with analyses of other (morphological, electrophoretic, karyotypic, immunological) data sets on these species. These data suggest that the reason for this continued difficulty lies in the timing of speciation events: the elapids apparently underwent a spectacular adaptive radiation soon after reaching Australia, such that divergences are ancient even within genera. Indeed, intrageneric divergences are almost as large as intergeneric divergences. Although this timing means that our sequence data cannot fully resolve phylogenetic relationships among the Australian elapids, the data suggest a close relationship of the following clades: Pseudonaja with Oxyuranus; Ogmodon with Toxicocalamus; Demansia with Aspidomorphus; Echiopsis with Denisonia; the "Notechis" lineage with Drysdalia coronoides; and Rhinoplocephalus and Suta with Drysdalia coronata. At least two of the Australian genera (Drysdalia and Simoselaps) appear to be paraphyletic. These sequence data support many of the conclusions reached by earlier studies using other types of data, but additional information will be needed before the phylogeny of the Australian elapids can be fully resolved.
Ecological causes for the evolution of sexual dimorphism: a review of the evidence.
Can sexual dimorphism evolve because of ecological differences between the sexes? Although several examples of this phenomenon are well known from studies on birds, the idea has often been dismissed as lacking general applicability. This dismissal does not stem from contradictory data so much as from the difficulties inherent in testing the hypothesis, and its apparent lack of parsimony, in comparison to the alternative explanation of sexual selection. The only unequivocal evidence for the evolution of sexual dimorphism through intersexual niche partitioning would be disproportionate dimorphism in trophic structures (e.g., mouthparts). This criterion offers a minimum estimate of the importance of ecological causes for dimorphism, because it may fail to identify most cases. A review of published literature reveals examples of sexually dimorphic trophic structures in most animal phyla. Many of these examples seem to be attributable to sexual selection, but others reflect adaptations for niche divergence between the sexes. For example, dwarf non-feeding males without functional mouthparts have evolved independently in many taxa. In other cases, males and females differ in trophic structures apparently because of differences in diets. Such divergence may often reflect specific nutritional requirements for reproduction in females, or extreme (sexually selected?) differences between males and females in habitats or body sizes. Ecological competition between the sexes may be responsible for intersexual niche divergence in some cases, but the independent evolution of foraging specializations by each sex may be of more general importance. If ecological causation for dimorphism can be demonstrated in so many cases, despite the inadequacies of the available criteria, the degree of sexual size dimorphism in many other animal species may well also have been influenced by ecological factors. Hence, it may be premature to dismiss this hypothesis, despite the difficulty of testing it.
Paternity and the evolution of male parental care.
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Propagule size and parental care: the "safe harbor" hypothesis.
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Methaemoglobin and its reduction in nucleated erythrocytes from reptiles and birds.
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MHC variation in birds and reptiles.
The major histocompatibility complex (MHC) has been studied in a multitude of mammals by now, but much less is known about its organisation and variation in other vertebrate species. The mammalian MHC is organised as a single gene cluster, but recent studies on birds suggest that this paradigm of MHC organisation has to be supplemented. The domestic chicken thus possesses two separate gene clusters which both contain MHC class I and class II B genes, and we have shown that the ring-necked pheasant Phasianus colchicus also has two unlinked clusters of class II B genes. We are studying the effect of the MHC on mate choice, survival and reproductive success in natural populations of birds and reptiles. For this reason, we are developing DNA techniques to determine the animals' MHC genotype. The amplification of the hypervariable exon 3 of the class I gene from songbirds and reptiles has provided us with species specific probes that can be used in Southern blot analysis. The first results indicate very extensive variation in all studied species, that is starlings Sturnus vulgaris, great reed warblers Acrocephalus arundinaceus and water pythons Liasis fuscus. The restriction fragment length polymorphism (RFLP) analysis also suggests that the number of MHC genes is significantly larger in these species than in pheasants and domestic chickens.
Conflicts between courtship and thermoregulation: the thermal ecology of amorous male garter snakes (Thamnophis sirtalis parietalis, colubridae).
Thermoregulatory behavior is an important component of daily activities for many reptiles, especially for small heliothermic (sun-basking) species that inhabit cold climates. However, the relative costs and benefits of thermoregulation depend on numerous factors, such that reptiles may sometimes accord a low priority to precise control of body temperatures. We observed and radio tracked garter snakes (Thamnophis sirtalis parietalis) in central Manitoba during the mating season (spring). Previous studies on this species have documented precise behavioral regulation of body temperatures during summer. In contrast, the courting snakes that we studied in springtime spent little time in overt thermoregulatory behavior. Body temperatures were extremely variable (both in outdoor enclosures and in the field) despite abundant opportunities for more precise thermal control. These small elongate reptiles cool so quickly (relative to the time periods needed for effective courtship) that any benefit to higher body temperatures would be transitory at best. Experiments show that hotter males are no better at obtaining matings or at detecting predators. Thus, male garter snakes concentrate on courtship rather than on basking. In the face of conflicting priorities, reptiles may often forgo precise thermoregulation because its benefits are too low, and its costs too high, compared with alternative behaviors.
Thermoregulation by a nocturnal elapid snake (Hoplocephalus bungaroides) in southeastern Australia.
Studies of reptilian thermoregulation have tended to focus on diurnal heliothermic taxa that display overt thermoregulatory behavior, with nocturnal reptiles attracting less attention. We studied thermoregulation by the broad-headed snake (Hoplocephalus bungaroides), a small (mean snout-vent length = 57 cm) nocturnal elapid that spends long periods sequestered in diurnal retreat sites. The snakes selected body temperatures of 28.1 degrees-31.1 degrees C in laboratory thermal gradients. Prey-capture ability (strike speed and accuracy) increased at higher body temperatures over the range 20 degrees-30 degrees C. Using temperature-sensitive radio transmitters, we obtained 7,801 body-temperature measurements of 19 free-ranging snakes. Information on operative environmental temperatures was obtained at the same time. From these data, we quantified the degree to which the snakes exploit the environmental thermal heterogeneity available to them (i.e., the time they spent within their set-point range, relative to the total time that these body temperatures were available to them). Mean body temperatures (both diurnally and nocturnally) differed among seasons but not among different types of retreat sites. Inclement weather prevented snakes from attaining "preferred" body temperatures on 30% of days. However, even when preferred temperatures were available, the snakes exploited this opportunity for only 26% of the time: they remained within retreat sites and rarely emerged to bask. Nonetheless, judicious retreat-site selection resulted in snakes being within their set-point range for 60% of the time at the most crucial time of day (i.e., the 2-h period around dusk, when the opportunity to capture prey is highest). Basking may be rare not only because of its high potential costs (e.g., risk of avian predation) but also because high body temperatures enhance snake fitness for only a short time each day and can be attained over that short period without the "expense" of heliothermy. Our results suggest that precise thermoregulation may not be widespread among snakes, particularly small nocturnal species that spend long periods sequestered in retreat sites.