Estimating field metabolic rates for Australian marsupials using phylogeny

Field metabolic rate (FMR) is a useful measure for the energy expenditure in free-ranging animals. Field metabolic rates for species that have not been measured are usually predicted by allometric equations on the basis of their body mass (BM). Phylogenetically informed methods improve estimates of both allometric relationships and species-specific FMR values by considering the evolutionary history of species. Further improvement is possible by incorporating isolated measurements on BM and FMR, but most existing methods force the user to discard such incomplete data. In the present study the FMR of most Australian marsupial species was predicted for the first time using a phylogenetic method that was explicitly designed to handle incomplete data. This allows full use of the dataset containing 35 samples of FMR and 130 samples of BM. Cross-validation demonstrated that FMRs were estimated with high accuracy. The resulting prediction equation was FMR (kJ day^? 1) = 5.27 BM (g)^0.69. Field metabolic rate and BM were highly phylogenetically correlated (r = 0.96), i.e. FMR and BM co-evolved. Differences between species-specific and generic marsupial estimates of FMR revealed that herbivores have lower energy expenditure than carnivores. Specifically, herbivorous macropods have on average lower relative FMR (kJ/d) (3.75 ± 0.53 BM^0.69; mean ± SD) than carnivorous dasyurids (7.64 ± 0.84 BM^0.69). Phylogenetically informed estimates for most extant Australian marsupial species are now available.     

Metabolic capacity and the evolution of biogeographic patterns in oscine and suboscine passerine birds

Biogeographic analyses of passerine birds demonstrate that suboscines are numerically dominant in South America, whereas oscines are dominant elsewhere. This suggests that oscines generally outcompete suboscines and that suboscine dominance likely persists in South America because of its long isolation from other continents, where oscines have diversified. One hypothesis for oscine competitive superiority is that oscines possess higher metabolic capacities than suboscines, and this favors oscines in most habitats. We tested this hypothesis by comparing summit metabolic rates (M(sum), maximum thermoregulatory metabolic rate) between oscines and suboscines using conventional and phylogenetically informed statistical approaches. We predicted that if the metabolic-capacity hypothesis is valid, then oscines should have higher M(sum) than suboscines. Both conventional and phylogenetically informed ANCOVA on regressions of log M(sum) against log mass showed that oscines had higher M(sum) than suboscines: least squares mean M(sum) was 74% greater for oscines. Moreover, conventional and phylogenetically informed multiple regressions identified log mass, winter-range temperature, and clade (oscines vs. suboscines) as significant effectors of log M(sum). Thus, oscines have generally higher M(sum) than suboscines, which is consistent with the metabolic-capacity hypothesis and suggests that metabolic capacity is one factor influencing the evolution of broad biogeographical patterns in passerines.     

Diet quality does not affect resting metabolic rate or body temperatures selected by an herbivorous lizard

Diet quality can influence many aspects of digestion, but the links between diet quality and resting metabolism are poorly understood. In nature, it might be beneficial to reduce energy expenditure when only poor quality diets are available. Alternatively, animals might increase the processing capacity of the gut to more thoroughly extract energy. If maintaining the processing capacity of the gut is energetically expensive, then increasing gut size or function might result in higher resting metabolism. In ectotherms, most digestive functions are temperature dependent, thus another strategy to maintain energy balance might be to alter selected body temperatures. We tested whether differing concentrations of dietary fiber affected the resting metabolic rate or body temperatures selected by chuckwallas (Sauromalus obesus) – lizards that naturally experience marked variation in dietary fiber. Resting metabolic rates measured at two temperatures and over three time intervals did not differ between groups of lizards force-fed low- (30% neutral-detergent fiber; NDF) and high-fiber (45% NDF) diets, nor did these diet differences influence body temperatures selected in a thermal gradient. We conclude that ecologically relevant differences in diet quality may have negligible effects on resting metabolic rates and body temperatures selected by chuckwallas. Accepted: 5 January 1998     

An exploration of differences in the scaling of life history traits with body mass within reptiles and between amniotes

Allometric relationships linking species characteristics to body size or mass (scaling) are important in biology. However, studies on the scaling of life history traits in the reptiles (the nonavian Reptilia) are rather scarce, especially for the clades Crocodilia, Testudines, and Rhynchocephalia (single extant species, the tuatara). Previous studies on the scaling of reptilian life history traits indicated that they differ from those seen in the other amniotes (mammals and birds), but so far most comparative studies used small species samples and also not phylogenetically informed analyses. Here, we analyzed the scaling of nine life history traits with adult body mass for crocodiles (n = 22), squamates (n = 294), turtles (n = 52), and reptiles (n = 369). We used for the first time a phylogenetically informed approach for crocodiles, turtles, and the whole group of reptiles. We explored differences in scaling relationships between the reptilian clades Crocodilia, Squamata, and Testudines as well as differences between reptiles, mammals, and birds. Finally, we applied our scaling relationships, in order to gain new insights into the degree of the exceptionality of the tuatara's life history within reptiles. We observed for none of the life history traits studied any difference in their scaling with body mass between squamates, crocodiles, and turtles, except for clutch size and egg weight showing small differences between these groups. Compared to birds and mammals, scaling relationships of reptiles were similar for time‐related traits, but they differed for reproductive traits. The tuatara's life history is more similar to that of a similar‐sized turtle or crocodile than to a squamate.     

The influence of temperature,sexual condition,and season on the metabolic rate of the lizardPsammodromus hispanicus

Summary Male and femalePsammodromus hispanicus from southern Europe were acclimated to four seasonal conditions of photoperiod and night time temperature. During the dark period, the lizards' body temperatures fell to ambient air temperature but during the light period the lizards were allowed to thermoregulate behaviourally and at such times the lizards' mean body temperature varied from 29.0°C to 32.6°C. The resting metabolic rate of these lizards was measured in 5°C steps from 5°C to 30°C or 35°C. Sexual condition had little effect on resting metabolic rate, but at low temperatures lizards acclimated to winter or spring seasonal conditions had lower resting metabolic rates than those acclimated to summer or autumn conditions. At temperatures above 20°C seasonal acclimation had no effect on resting metabolic rate. It is considered that the reduction in low temperature metabolic rate in spring and winter is induced by low night time temperatures and serves to conserve energy during those seasons when lizards must spend long periods at low temperature without being able to feed.     

Behavioral buffering of global warming in a cold‐adapted lizard

Alpine lizards living in restricted areas might be particularly sensitive to climate change. We studied thermal biology of Iberolacerta cyreni in high mountains of central Spain. Our results suggest that I. cyreni is a cold‐adapted thermal specialist and an effective thermoregulator. Among ectotherms, thermal specialists are more threatened by global warming than generalists. Alpine lizards have no chance to disperse to new suitable habitats. In addition, physiological plasticity is unlikely to keep pace with the expected rates of environmental warming. Thus, lizards might rely on their behavior in order to deal with ongoing climate warming. Plasticity of thermoregulatory behavior has been proposed to buffer the rise of environmental temperatures. Therefore, we studied the change in body and environmental temperatures, as well as their relationships, for I. cyreni between the 1980s and 2012. Air temperatures have increased more than 3.5°C and substrate temperatures have increased by 6°C in the habitat of I. cyreni over the last 25 years. However, body temperatures of lizards have increased less than 2°C in the same period, and the linear relationship between body and environmental temperatures remains similar. These results show that alpine lizards are buffering the potential impact of the increase in their environmental temperatures, most probably by means of their behavior. Body temperatures of I. cyreni are still cold enough to avoid any drop in fitness. Nonetheless, if warming continues, behavioral buffering might eventually become useless, as it would imply spending too much time in shelter, losing feeding, and mating opportunities. Eventually, if body temperature exceeds the thermal optimum in the near future, fitness would decrease abruptly.     

Direct effects of incubation temperature on morphology,thermoregulatory behaviour and locomotor performance in jacky dragons (Amphibolurus muricatus)

Incubation temperature is one of the most studied factors driving phenotypic plasticity in oviparous reptiles. We examined how incubation temperature influenced hatchling morphology, thermal preference and temperature-dependent running speed in the small Australian agamid lizard Amphibolurus muricatus. Hatchlings incubated at 32 °C grew more slowly than those incubated at 25 and 28 °C during their first month after hatching, and tended to be smaller at one month. These differences were no longer significant by three months of age due to selective mortality of the smallest hatchlings. The cooler incubation treatments (25 °C and 28 °C) produced lizards that had deeper and wider heads. Hatchlings from 28 °C had cooler and more stable temperature preferences, and also had lower body temperatures during a 2-h thermoregulatory behaviour trial. Locomotor performance was enhanced at higher body temperatures, but incubation temperature had no measurable effect either independently or in interaction with body temperature. Our study demonstrates that incubation temperature has direct effects on morphology and thermoregulatory behaviour that appears to be independent of any size-dependent effects. We postulate a mechanistic link between these two effects.     

The link between metabolic rate and body temperature in galliform birds in thermoneutral and heat exposure conditions: The classical and phylogenetically corrected approach

Three galliform species (grey partridges, ring-necked pheasants, and king quail) were involved in body temperature and resting metabolic rate measurements over a broad range of ambient temperatures (20–45 °C). At thermoneutrality, inter-species differences in colonic temperature, as well as in metabolic rate, were observed. During heat exposure, all species reacted by elevating their body temperatures above 44 °C, thereby inducing temporary hyperthermia. Heat-stressing birds resulted in a slightly increased metabolic rate in king quail, but not in partridges and pheasants. Based on data of body temperature and weight specific (per body mass unit) basal metabolic rate among ten species of Galliformes order, classical and phylogenetically corrected analyses of covariation between these two physiological traits were performed. The scaling of body temperature to body mass, revealed a significant exponent of: −0.0062 and −0.0080 for conventional and phylogenetical methods, respectively. In the analyzed species, a strong positive relationship between residuals of body mass values between body temperature and metabolic rate were found. The results obtained may show a plausible evolutionary link between these traits in galliform birds.     

Metabolic, hygric and ventilatory physiology of a hypermetabolic marsupial, the honey possum (Tarsipes rostratus)

The honey possum is the only non-volant mammal to feed exclusively on a diet of nectar and pollen. Like other mammalian and avian nectarivores, previous studies indicated that the honey possum’s basal metabolic rate was higher than predicted for a marsupial of equivalent body mass. However, these early measurements have been questioned. We re-examined the basal metabolic rate (2.52 ± 0.222 ml O₂ g⁻¹ h⁻¹) of the honey possum and confirm that it is indeed higher (162%) than predicted for other marsupials both before and after accounting for phylogenetic history. This, together with its small body mass (5.4 ± 0.14 g; 1.3% of that predicted by phylogeny) may be attributed to its nectarivorous diet and mesic distribution. Its high-basal metabolic rate is associated with a high-standard body temperature (36.6 ± 0.48°C) and oxygen extraction (19.4%), but interestingly the honey possum has a high point of relative water economy (17.0°C) and its standard evaporative water loss (4.33 ± 0.394 mg H₂O g⁻¹ h⁻¹) is not elevated above that of other marsupials, despite its mesic habitat and high dietary water intake.     

Resting metabolism of helodermatid lizards: allometric and ecological relationships

We measured metabolic rates at 15 and 25°C in 42 helodermatid lizards ranging in mass from 26 to 1616 g. No consistent repeatable daily rhythms of metabolism were detected. There were no significant differences in metabolic rates between the two species of Heloderma. The temperature coefficient for metabolism (Q ₁₀) was 3.0 between 15 and 25°C. The mass exponent for helodermatids (0.69) differed significantly from the among-species mass exponent of 0.80 for all squamates combined. However, adult Heloderma had a mass exponent of 0.80. Rates of metabolism of adult helodermatids were lower than those of other squamate reptiles, and at 15°C periods of apnea contributed to a further reduction in metabolic rate. Our finding that helodermatids have low SMRs supports the hypothesis that ecology is important in influencing metabolic rate, and that “reclusive” squamates have lower rates of metabolism than do nonreclusive species.     

Measurement of the rate of protein turnover and synthesis in the marsupial Honey possum (<Emphasis Type="Italic">Tarsipes rostratus</Emphasis>)

Rates of protein turnover and synthesis were measured in wild-caught Honey possums (Tarsipes rostratus) in the southwest of Western Australia and compared between males and females with and without pouch young. Possums were injected with 50 μg of ¹⁵N-glycine and ammonia collected within 24 h was used as the nitrogen end-product in a single-injection protocol. The overall mean rate of protein synthesis measured was 7.7 ± 0.5 g kg^−0.75 day⁻¹, which falls within the range of values reported for other marsupial species. Whole body rates of nitrogen flux and protein synthesis did not vary significantly between males and females with and without young, but females with pouch young showed significantly lower rates of protein synthesis when expressed in relation to metabolic body size. This difference was no longer apparent, however, if the mass of the females was corrected for the estimated mass of the young in the pouch averaging 9.3 ± 1.6 g kg^−0.75 day⁻¹ and suggesting that the young should not be considered as part of the metabolic body pool. Whole body rates of protein degradation were significantly reduced in females carrying pouch young, suggesting that protein may be being diverted from the pool to milk production. Calculations indicate that the daily fraction of the female’s nitrogen synthesis rate that needs to be diverted to pouch young to sustain their growth is less than 5%, and may not be detectable with the current methodology.     

Differences in the thermal physiology of adult Yarrow's spiny lizards (Sceloporus jarrovii) in relation to sex and body size

Sexual size dimorphism (SSD) is often assumed to reflect the phenotypic consequences of differential selection operating on each sex. Species that exhibit SSD may also show intersexual differences in other traits, including field‐active body temperatures, preferred temperatures, and locomotor performance. For these traits, differences may be correlated with differences in body size or reflect sex‐specific trait optima. Male and female Yarrow's spiny lizards, Sceloporus jarrovii, in a population in southeastern Arizona exhibit a difference in body temperature that is unrelated to variation in body size. The observed sexual variation in body temperature may reflect divergence in thermal physiology between the sexes. To test this hypothesis, we measured the preferred body temperatures of male and female lizards when recently fed and fasted. We also estimated the thermal sensitivity of stamina at seven body temperatures. Variation in these traits provided an opportunity to determine whether body size or sex‐specific variation unrelated to size shaped their thermal physiology. Female lizards, but not males, preferred a lower body temperature when fasted, and this pattern was unrelated to body size. Larger individuals exhibited greater stamina, but we detected no significant effect of sex on the shape or height of the thermal performance curves. The thermal preference of males and females in a thermal gradient exceeded the optimal temperature for performance in both sexes. Our findings suggest that differences in thermal physiology are both sex‐ and size‐based and that peak performance at low body temperatures may be adaptive given the reproductive cycles of this viviparous species. We consider the implications of our findings for the persistence of S. jarrovii and other montane ectotherms in the face of climate warming.     

The influence of competitor density on space use in juvenile striped plateau lizards (Sceloporus virgatus)

To investigate the role of competitor density in influencing space use patterns of juvenile striped plateau lizards (Sceloporus virgatus), a density manipulation experiment was conducted within large (800 m²) field enclosures treated with low (20) and high (60) densities of hatchlings. Enclosures were monitored for 10 months, after which the experiment was replicated. Home range and core area sizes after release of lizards and initial establishment in the fall were significantly reduced in the high-density treatments; fall home range shape, measured as the perimeter-to-area ratio, was significantly reduced in low-density treatments; no significant differences were detected between treatments in core area shape or overlap. During the spring/early summer activity season after the lizard's first winter, no significant differences between density treatments were detected for any of these variables, as enclosure densities had converged between treatments. Individuals in high-density enclosures had increased their space use as competitor density had declined. These results illustrate that competitor density has significant influence on space use by juvenile lizards.     

Comparison of oxygen consumption in drosophilid flies from different climates

Oxygen consumption at rest was studied in drosophilid species from cool‐temperate, warm‐temperate and subtropical regions to assess whether adaptations to different climates are associated with changes in metabolic rates. In experiments at 23°C using 8‐day‐old males of 28 species, body mass was revealed to be a significant predictor of oxygen consumption. No significant relation was detected between mass‐adjusted oxygen consumption and latitudinal distribution or thermal tolerance by either conventional regression analysis or a phylogenetically based method. The effect of temperature on oxygen consumption was studied with experiments at 15, 18, 23 and 28°C using 8‐ and 24‐day‐old males of four species of each of the montium species subgroup and the subgenus Drosophila. In these experiments, it was confirmed that temperature was a significant predictor of mass‐adjusted oxygen consumption. In both lineages, mass‐adjusted oxygen consumption was not higher in cool‐temperate species than in subtropical species. Thus, adaptations to colder climates are not associated with elevation of metabolic rates in these drosophilid species. The results of the present study also indicate that oxygen consumption is not related to the capacity to walk quickly.     

Phylogenetic comparisons of pedestrian locomotion costs: confirmations and new insights

The energetic costs for animals to locomote on land influence many aspects of their ecology. Size accounts for much of the among‐species variation in terrestrial transport costs, but species of similar body size can still exhibit severalfold differences in energy expenditure. We compiled measurements of the (mass‐specific) minimum cost of pedestrian transport (COT_min, mL/kg/m) for 201 species – by far the largest sample to date – and used phylogenetically informed comparative analyses to investigate possible eco‐evolutionary differences in COT_min between various groupings of those species. We investigated number of legs, ectothermy and endothermy, waddling, and nocturnality specifically in lizards. Thus, our study primarily revisited previous theories about variations in COT_min between species, testing them with much more robust analyses. Having accounted for mass, while residual COT_min did not differ between bipedal and other species, specifically waddling bipeds were found to have relatively high COT_min. Furthermore, nocturnal lizards have relatively low COT_min although temperature does not appear to affect COT_min in ectotherms. Previous studies examining across‐species variation in COT_min from a biomechanical perspective show that the differences between waddling birds and nonwaddling species, and between nocturnal lizards and other ecotherms, are likely to be attributable to differences in ground reaction forces, posture, and effective limb length.     

Bergmann's Rule rules body size in an ectotherm: heat conservation in a lizard along a 2200‐metre elevational gradient

Bergmann's Rule predicts larger body sizes in colder habitats, increasing organisms' ability to conserve heat. Originally formulated for endotherms, it is controversial whether Bergmann's Rule may be applicable to ectotherms, given that larger ectotherms show diminished capacity for heating up. We predict that Bergmann's Rule will be applicable to ectotherms when the benefits of a higher conservation of heat due to a larger body size overcompensate for decreased capacity to heating up. We test this hypothesis in the lizard Psammodromus algirus, which shows increased body size with elevation in Sierra Nevada (SE Spain). We measured heating and cooling rates of lizards from different elevations (from 300 to 2500 m above sea level) under controlled conditions. We found no significant differences in the heating rate along an elevational gradient. However, the cooling rate diminished with elevation and body size: highland lizards, with larger masses, have a higher thermal inertia for cooling, which allows them to maintain heat for more time and keep a high body temperature despite the lower thermal availability. Consequently, the net gaining of heat increased with elevation and body size. This study highlights that the heat conservation mechanism for explaining Bergmann's Rule works and is applicable to ectotherms, depending on the thermal benefits and costs associated with larger body sizes.     

Shivering and non-shivering thermogenesis in a marsupial,the eastern barred bandicoot (Perameles gunnii)

We investigated the metabolic rate of the Tasmanian marsupial, the eastern barred bandicoot, Perameles gunnii, before and after acclimation to cold temperature (5 °C) for a 2-week period. Although body temperature did not change significantly, we observed a significant increase in the metabolic rate (MR) when measured at 5 °C before and after cold acclimation. Nor-epinephrine had a significant effect on the metabolic rate when measured in the thermoneutral zone and when measured at 5 °C after cold acclimation; however, there was no significant increase when measured at 5 °C before cold acclimation. Nor-epinephrine also resulted in a small but significant decrease in body temperature. Electromyography (EMG) measurements were obtained before and after cold acclimation during shivering. Shivering decreased after two weeks of cold exposure indicating that the bandicoot had acclimated to that temperature. Nor-epinephrine (NE) significantly reduced shivering before but not after cold acclimation. The metabolic rate and shivering decreased in the adult eastern barred bandicoot after acclimation at 5 °C and nor-epinephrine had similar effects to cold acclimation. Our findings of minor changes in thermal conductance suggest that insulation differences were unlikely explanations for our results. These experiments indicate that this marsupial is able to increase its heat production by non-shivering thermogenesis.     

Nocturnal lizards from a cool-temperate environment have high metabolic rates at low temperatures

Ectotherms from low-temperature environments have higher metabolic rates at low temperatures than those from warm-temperature environments. We predicted that nocturnal lizards, which are active at much lower environmental temperatures than diurnal lizards, would also have higher metabolic rates at low temperatures, and by association a lower thermal sensitivity (Q ₁₀) than diurnal and crepuscular lizards. We measured the rate of oxygen consumption ( [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} ) of eight cool-temperate species of lizard (four nocturnal, three diurnal, and one crepuscular) at 13 and 26°C and analyzed log transformations of these data using log mass as a covariate. As expected, [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} was positively correlated with temperature in all eight species, with [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} being two to four times higher at 26°C than at 13°C. As predicted, at 13°C (but not 26°C) the [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} was significantly higher in nocturnal than diurnal lizards. Species-specific differences and mass scaling factors explain the patterns of thermal sensitivity seen among these eight lizard species. Thermal sensitivity is strongly influenced by mass, with smaller species generally having higher thermal sensitivity of their metabolic rate, and this result deserves further exploration among other ectotherms. We conclude that, along with the previously reported lower cost of locomotion found in nocturnal lizards, they also partially offset the thermal handicap of activity at low body temperatures by having an elevated [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} at lower temperatures.     

Effects of terrigenous organic substrates and additional phosphorus on bacterioplankton metabolism and exoenzyme stoichiometry

1. Bamboo, as a pioneer vegetation, often forms forests on bare lands after catastrophic landslides. Compared to evergreen forest soil, bamboo forest soil is much more labile, with a higher percentage of microbially derived organic carbon (OC), lower molecular weight, and lower humic acid content. We hypothesised that different terrigenous organic matter (tOM) sources with varying lability and phosphorus (P) availability select for bacterioplankton with distinct metabolic pathways.
2. We incubated natural bacterioplankton assemblages with tOM leached from bamboo forest soil (BOM) and evergreen forest soil (EOM) and compared these to a lake water control. To test if microbial metabolism would be limited by OC or P availability of each tOM treatment, we used acetate as an extra labile OC source and phosphate as an inorganic P source. Bacterial metabolism was measured by analysing respiration via O₂ consumption and production via tritiated thymidine (TdR) assimilation.
3. Bacterioplankton metabolism is limited by the availability of P in BOM substrates. When using BOM, bacteria had higher enzymatic activities for phosphatase. The nutrients required for bacterial biomass seemed to be derived from organic matter. Under BOM treatment, bacterial production (BP) (0.92 ± 0.13 μg C L⁻¹ hr⁻¹) and cell specific TdR assimilation rates (0.015 ± 0.002 10^–18 M TdR cell⁻¹ hr⁻¹) were low. Adding P enhanced BP (BOM_+P 1.52 ± 0.31 and BOM_+C+P 2.25 ± 0.37 μg C L⁻¹ hr⁻¹) while acetate addition had no significant effect on BOM treatment.
4. This indicated that the bacteria switched to using added inorganic P to respire a P-limited BOM substrate, which increased total BP and abundance, resulting in even more active respiration and lower growth efficiency. We also found higher activities for chitin-degrading enzyme β-N-acetylglucosaminidase, which is associated with N mining from aminosaccharides.
5. Microbes using EOM, however, did not change metabolic strategies with additional acetate or/and inorganic P. This is due to higher concentrations of organic P in EOM substrates and the presence of inorganic N in the EOM leachates an alternative nutrient source. Bacteria produced β-glucosidase and leucyl-aminopeptidase in order to utilise the humic substances, which sustained greater bacterial abundance, higher BP (2.64 ± 0.39 μg C L⁻¹ hr⁻¹), and lower cell-specific respiration. This yielded a much higher bacterial growth efficiency (15 ± 9.2%) than the lake water control.
6. Our study demonstrated the aquatic metabolic discrepancy between tOM of different forest types. Bacterioplankton in BOM and EOM exhibit distinct metabolic responses. Bacterial metabolic strategy when using BOM implied that the supposedly stabilised biomass OM might be efficiently used by aquatic bacterioplankton. As the labile and nutrient-deficient BOM is more susceptible to the influence of additional nutrients, fertiliser residues in bamboo forest catchments might have a stronger effect on aquatic bacterial metabolic pathways. Thus, it is important to take tOM differences into consideration when building models to estimate soil carbon turnover rates along a terrestrial–aquatic continuum.

     

Host specificity shapes population structure of pinworm parasites in Caribbean reptiles

Host specificity is one of the potential factors affecting parasite diversification because gene flow may be facilitated or constrained by the number of host species that a parasite can exploit. We test this hypothesis using a costructure approach, comparing two sympatric pinworm parasites that differ in host specificity – Parapharyngodon cubensis and Spauligodon anolis – on the Puerto Rican Bank and St. Croix in the Caribbean. Spauligodon anolis specializes on Anolis lizards, whereas P. cubensis parasitizes Anolis lizards as well as many other species of lizards and snakes. We collected lizards from across the Puerto Rican Bank and St. Croix, sampled them for S. anolis and P. cubensis and generated nuclear and mitochondrial sequence data from the parasites. We used these data to show that P. cubensis is comprised of multiple cryptic species that exhibit limited population structure relative to S. anolis, which is consistent with our prediction based on their host specificity. We also provide evidence that the distribution of P. cubensis species is maintained by competitive exclusion, and in contrast to previous theoretical work, the parasites with the greatest number of host species also reach the highest prevalence rates. Overall, our results are consistent with the hypothesis that host specificity shapes parasite diversification, and suggest that even moderate differences in host specificity may contribute to substantial differences in diversification.