Use of immunohistochemistry to diagnose chytridiomycosis in dyeing poison dart frogs (Dendrobates tinctorius)

Chytridiomycosis, caused by Batrachochytrium dendrobatidis, is an emerging disease of both wild and captive amphibians, posing a threat to their survival in many parts of the world. As the disease can be difficult to diagnose on routine pathologic sections, the purpose of this study was to develop an additional method for visualization. To accomplish this, immunohistochemical staining was applied to histologic skin sections from four experimentally infected Dyeing poison dart frogs (Dendrobates tinctorius). Staining of the positive tissue sections was distinct and readily visualized, making this technique a valuable ancillary diagnostic test for this important disease.     

Evolution of parental care in dart poison frogs (Amphibia: Anura: Dendrobatidae)

Dendrobatid frogs perform a unique mode of parental care, ranging from egg attendance and tadpole transport to tadpole feeding. It is hypothesized that a behaviour in which the egg attending parent remains with the cluch is the most primitive condition. In more advanced forms or parental care, the male is able to attend several clutches of eggs. Tadpole attendance and feeding, finally, started as deceit; the male induced the female to lay eggs into a bromeliad leaf axil already occupied by a larva. Costs and benefits of the different modes of parental care and possible alternative reproductive tactics are discussed.     

Growth and body size in populations of mink frogs Rana septentrionalis from two latitudes

Age, longevity, and growth in mink frogs Rana septentrionalis from two latitudes in Quebec, Canada, were assessed by skeletochronological and back-calculation methods in order to document proximate causes for intraspecific variations in adult body size. In both study sites, females grew faster and were on average 11% larger than males. Mean age and maximal longevity were significantly higher in females than in males only in the southern populations. There was thus an interpopulation difference in the relative contribution of age and growth to sexual size dimorphisms. Sex-ratio also favored females (males sulfering higher mortality) only in the southern populations. Specimens from the northern population had higher mean ages (but not higher longevities) and were 17% larger than specimens from the southern populations. Annual growth rate appeared similar at the two study sites despite a shorter growing season at the northern locality. Maturity was reached by both sexes after 1 yr of post-metamorphic life (PML) in the southern populations but after 2 yr of PML in the northern population. There are indications that tadpoles metamorphose at larger body size at the northern locality after a prolonged larval period. It is concluded that growth rate, delayed maturity, greater mean ages, and eventually size at transformation, all contribute to the larger size of adult mink frogs at northern localities.     

Parasite infection has little effect on sexual signals and reproductive behaviour in strawberry poison frogs

Acoustic and visual signals like mating calls or colour patterns, which are involved in courtship displays, can be affected by the health status of an individual. For example, infection with parasites can result in sexual signals that are less intense or conspicuous than in healthy individuals; thus it is generally assumed that sexual signals indicate the quality of the holder. We use strawberry poison frogs from Costa Rica to find out (1) whether there is variation in the parasite load among individuals, (2) whether the parasite load varies over time, (3) whether the parasite load has an effect on acoustic and visual signals, which are supposed to be important for female mate choice and (4) whether the parasite load influences the reproductive behaviour. We found that 60 % of our focal males were infested with an intestinal nematode of the genus Cosmocerca while the parasite load changed considerably over time. We found slight associations between the intensity of acoustic signals (advertisement calls), visual signals (colour and brightness contrasts) and parasite load. Non-infected males produced significantly lower pulse rates than parasitised males. As pulse rate has been shown to decrease with age, we suggest that males without parasites become older than infected males. Moreover, the visual contrasts of the frogs varied across natural backgrounds. An interaction between parasite infection and the background of the calling place affected the ventral colour contrast. This finding suggests that at least some males without parasites defend calling places that render them more conspicuousness to conspecifics than other potential positions would. There were no differences in several elements of reproductive behaviour between parasitised and healthy males. Further studies are necessary to find out whether parasite infection varies among populations, and whether at higher levels it would have a stronger influence on sexual signals, behaviour and lifetime fitness.     

Ultrastructure of the dermal chromatophores in a lizard (Scincidae: Plestiodon latiscutatus) with conspicuous body and tail coloration

Microscopic observation of the skin of Plestiodon lizards, which have body stripes and blue tail coloration, identified epidermal melanophores and three types of dermal chromatophores: xanthophores, iridophores, and melanophores. There was a vertical combination of these pigment cells, with xanthophores in the uppermost layer, iridophores in the intermediate layer, and melanophores in the basal layer, which varied according to the skin coloration. Skin with yellowish-white or brown coloration had an identical vertical order of xanthophores, iridophores, and melanophores, but yellowish-white skin had a thicker layer of iridophores and a thinner layer of melanophores than did brown skin. The thickness of the iridophore layer was proportional to the number of reflecting platelets within each iridophore. Skin showing green coloration also had three layers of dermal chromatophores, but the vertical order of xanthophores and iridophores was frequently reversed. Skin showing blue color had iridophores above the melanophores. In addition, the thickness of reflecting platelets in the blue tail was less than in yellowish-white or brown areas of the body. Skin with black coloration had only melanophores.     

The evolution of conspicuous coloration: Some experiments in bad taste

Unpalatable species are often brightly coloured. Such aposematic coloration may have evolved because predators can learn to avoid conspicuous prey more readily than cryptic prey. Experiments on young male chicks are described and the results are consistent with this hypothesis.     

A test of an antipredatory function of conspicuous plastron coloration in hatchling turtles

Bright colorations in animals are sometimes an antipredatory signal meant to startle, warn, or deter a predator from consuming a prey organism. Freshwater turtle hatchlings of many species have bright ventral coloration with high internal contrast that may have an antipredator function. We used visual modeling and field experiments to test whether the plastron coloration of Chrysemys picta hatchlings deters predators. We found that bird predators can easily distinguish hatchling turtles from their backgrounds and can easily see color contrast within the plastron. Raccoons cannot easily discriminate within-plastron color contrast but can see hatchlings against common backgrounds. Despite this, we found that brightly-colored, high contrast, replica turtles were not attacked less than low contrast replica turtles, suggesting that the bright coloration is not likely to serve an antipredatory function in this context. We discuss the apparent lack of innate avoidance of orange coloration in freshwater turtles by predators and suggest that preference and avoidance of colors are context-dependent. Since the bright colors are likely not a signal, we hypothesize that the colors may be caused by pigments deposited in tissue from maternal reserves during development. In most species, these pigments fade ontogenetically but they may have important physiological functions in species that maintain the bright coloration throughout adulthood.     

Fast molecular evolution associated with high active metabolic rates in poison frogs

Molecular evolution is simultaneously paced by mutation rate, genetic drift, and natural selection. Life history traits also affect the speed of accumulation of nucleotide changes. For instance, small body size, rapid generation time, production of reactive oxygen species (ROS), and high resting metabolic rate (RMR) are suggested to be associated with faster rates of molecular evolution. However, phylogenetic correlation analyses failed to support a relationship between RMR and molecular evolution in ectotherms. In addition, RMR might underestimate the metabolic budget (e.g., digestion, reproduction, or escaping predation). An alternative is to test other metabolic rates, such as active metabolic rate (AMR), and their association with molecular evolution. Here, I present comparative analyses of the associations between life history traits (i.e., AMR, RMR, body mass, and fecundity) with rates of molecular evolution of and mitochondrial loci from a large ectotherm clade, the poison frogs (Dendrobatidae). My results support a strong positive association between mass-specific AMR and rates of molecular evolution for both mitochondrial and nuclear loci. In addition, I found weaker and genome-specific covariates such as body mass and fecundity for mitochondrial and nuclear loci, respectively. No direct association was found between mass-specific RMR and rates of molecular evolution. Thus, I provide a mechanistic hypothesis of the link between AMRs and the rate of molecular evolution based on an increase in ROS within germ line cells during periodic bouts of hypoxia/hyperoxia related to aerobic exercise. Finally, I propose a multifactorial model that includes AMR as a predictor of the rate of molecular evolution in ectothermic lineages.     

Insular shifts in body size of rice frogs in the Zhoushan Archipelago, China

1. Differences in body size between mainland and island populations have been reported for reptiles, birds and mammals. Despite widespread recognition of insular shifts in body size in these taxa, there have been no reports of such body size shifts in amphibians. 2. We provide the first evidence of an insular shift in body size for an amphibian species, the rice frog Rana limnocharis. We found significant increases in body size of rice frogs on most sampled islands in the Zhoushan archipelago when compared with neighbouring mainland China. 3. Large body size in rice frogs on islands was significantly related to increased population density, in both breeding and non-breeding seasons. Increases in rice frog density were significantly related to higher resource availability on islands. Increased resource availability on islands has led to higher carrying capacities, which has subsequently facilitated higher densities and individual growth rates, resulting in larger body size in rice frogs. We also suggest that large body size has evolved on islands, as larger individuals are competitively superior under conditions of harsh intraspecific competition at high densities. 4. Increases in body size in rice frogs were not related to several factors that have been implicated previously in insular shifts in body size in other taxa. We found no significant relationships between body size of rice frogs and prey size, number of larger or smaller frog species, island area or distance of islands from the mainland. 5. Our findings contribute to the formation of a broad, repeatable ecological generality for insular shifts in body size across a range of terrestrial vertebrate taxa, and provide support for recent theoretical work concerning the importance of resource availability for insular shifts in body size.     

Evolution of conspicuous colouration, body size and gregariousness: a comparative analysis of lepidopteran larvae

Protective colouration in animals includes camouflage (i.e., crypsis), that decreases the risk of detection, and conspicuous colouration, which is often used in combination with chemical defences to deter predators from attacking. Experiments have shown that the efficacy of conspicuous colouration increases with increasing size of pattern elements and larger body size. Prey species that have acquired avoidance inducing colouration therefore may be exposed to selection for larger body size, and such colouration may more easily evolve in large than in small prey species. Here we test for a difference in body size between species with different colouration modes and perform a comparative analysis based on phylogenetically independent contrasts to examine if evolutionary shifts in colour pattern have been associated with evolutionary changes in body size, using data for 578 species of moths. Larval body size did not differ between species with signalling and non-signalling larvae, and results from the comparative analysis suggest that these two traits have not evolved in parallel. The lack of association between evolutionary changes in colouration and body size may reflect a confounding influence of lifestyle, because evolutionary shifts from solitary to group-living larvae were associated with decreased larval body length and adult wing span. Because evolutionary changes in larval body size were associated with evolutionary changes in adult wing span the predicted association between colouration and size may have been confounded also by conflicting selection on body size in larvae and adults.     

Thermal constraints for stingless bee foragers: the importance of body size and coloration

In the dry tropics, foraging bees face significant thermal constraints as a result of high ambient temperatures and direct insolation. In order to determine the potential importance of body size and body coloration in heat gain and heat loss, passive warm-up and cooling rates were measured for freshly killed workers of 24 stingless bee species. Results accorded with biophysical principles. Small bees reached lower temperature excesses (T_exc) and warmed up and lost heat much more rapidly than larger bees. In addition to body size, body coloration had a clear effect on thermal parameters. Light-coloured bees warmed up less rapidly and had lower T_exc than dark bees. An intraspecific comparison of Melipona costaricensis and Cephalotrigona capitata colour morphs confirmed that body coloration influences thermal characteristics. This study is the first to indicate that abdominal coloration in stingless bees might be involved in the regulation of body temperature in extreme thermal conditions. However, body temperatures of foraging bees of colour morphs were not very different. This is probably due to behavioural adaptations (e.g. foraging strategies) or differences in convective and evaporative heat loss or the production of metabolic heat during flight, that all mask the effect of body colour. Notwithstanding such effects and potential thermoregulatory capabilities, stingless bees show niche differentiation and biogeographic distributions that correlate with body coloration and body size. This also suggests that, in general, light bees have an advantage over black bees in hot open lowland habitats, whereas black bees might have an advantage in wet habitats and mountains. The origin, occurrence and function of flavinism (yellow integument colouring) are discussed.     

Elevational patterns of species richness, range and body size for spiny frogs

Quantifying spatial patterns of species richness is a core problem in biodiversity theory. Spiny frogs of the subfamily Painae (Anura: Dicroglossidae) are widespread, but endemic to Asia. Using spiny frog distribution and body size data, and a digital elevation model data set we explored altitudinal patterns of spiny frog richness and quantified the effect of area on the richness pattern over a large altitudinal gradient from 0-5000 m a.s.l. We also tested two hypotheses: (i) the Rapoport's altitudinal effect is valid for the Painae, and (ii) Bergmann's clines are present in spiny frogs. The species richness of Painae across four different altitudinal band widths (100 m, 200 m, 300 m and 400 m) all showed hump-shaped patterns along altitudinal gradient. The altitudinal changes in species richness of the Paini and Quasipaini tribes further confirmed this finding, while the peak of Quasipaini species richness occurred at lower elevations than the maxima of Paini. The area did not explain a significant amount of variation in total, nor Paini species richness, but it did explain variation in Quasipaini. Five distinct groups across altitudinal gradient were found. Species altitudinal ranges did not expand with an increase in the midpoints of altitudinal ranges. A significant negative correlation between body size and elevation was exhibited. Our findings demonstrate that Rapoport's altitudinal rule is not a compulsory attribute of spiny frogs and also suggest that Bergmann's rule is not generally applicable to amphibians. The study highlights a need to explore the underlying mechanisms of species richness patterns, particularly for amphibians in macroecology.     

Protein polymorphism in quail populations selected for large body size

The polymorphism of five enzyme loci (amylase, alkaline phosphatase, albumin, for 4-week body weight was compared to that of the unselected control line (C). for 4 week body weight was compared to that of the unselected control line (C). Three loci in the C line and two in the P line demonstrated polymorphism. Plasma amylase was separated into six bands and zymograms were classified on the basis of these bands into nine phenotypes. Three of the nine types were of relatively high activity and six were of relatively low activity. All nine types were found in the C line, whereas, all birds of the P line had only the most active type. Two alkaline phosphatase alleles (Akp-2^B and Akp-2^C) were segregating in the C line. Gene frequencies of alkaline phosphatase for the Akp-2^B allele were 0.92 in the C line and 1.00 in the P line. Two albumin alleles (Alb^Q1 and Alb^Q2) were segregating in both populations. Gene frequencies for the Alb^Q1 allele were 0.74 in the C line and 0.81 in the P line. Two red cell esterase-D alleles (Es-D^F and Es-D^s) were segregating in both populations. The gene frequency for the Es-D^s allele (0.61) was higher than that of the Es-D^F allele in the C line. In the P line the frequency of the Es-D^F allele was higher than that of the Es-D^s allele. Heterozygosities of the C and P lines were estimated as 0.2258 and 0.1560 respectively. The relative inbreeding coefficient of the P line, calculated from heterozygosities was 0.31.     

Protein polymorphism in quail populations selected for large body size

The polymorphism of five enzyme loci (amylase, alkaline phosphatase, albumin, for 4-week body weight was compared to that of the unselected control line (C). Three loci in the C line and two in the P line demonstrated polymorphism. Plasma amylase was separated into six bands and zymograms were classified on the basis of these bands into nine phenotypes. Three of the nine types were of relatively high activity and six were of relatively low activity. All nine types were found in the C line, whereas, all birds of the P line had only the most active type. Two alkaline phosphatase alleles (Akp-2B and Akp-2C) were segregating in the C line. Gene frequencies of alkaline phosphatase for the Akp-2B allele were 0.92 in the C line and 1.00 in the P line. Two albumin alleles (AlbQ1 and AlbQ2) were segregating in both populations. Gene frequencies for the AlbQ1 allele were 0.74 in the C line and 0.81 in the P line. Two red cell esterase-D alleles (Es-DF and Es-DS) were segregating in both populations. The gene frequency for the Es-DS allele (0.61) was higher than that of the Es-DF allele in the C line. In the P line the frequency of the Es-DF allele was higher than that of the Es-DS allele. Heterozygosities of the C and P lines were estimated as 0.2258 and 0.1560 respectively. The relative inbreeding coefficient of the P line, calculated from heterozygosities was 0.31.     

Testing for microevolution in body size in three blue tit populations

Quantifying the genetic variation and selection acting on phenotypes is a prerequisite for understanding microevolutionary processes. Surprisingly, long-term comparisons across conspecific populations exposed to different environments are still lacking, hampering evolutionary studies of population differentiation in natural conditions. Here, we present analyses of additive genetic variation and selection using two body-size traits in three blue tit (Parus caeruleus) populations from distinct habitats. Chick tarsus length and body mass at fledging showed substantial levels of genetic variation in the three populations. Estimated heritabilities of body mass increased with habitat quality. The poorer habitats showed weak positive selection on tarsus length, and strong positive selection on body mass, but there was no significant selection on either trait in the good habitat. However, there was no evidence of any microevolutionary response to selection in any population during the study periods. Potential explanations for this absence of a response to selection are discussed, including the effects of spatial heterogeneity associated with gene flow between habitats.     

Ornament and body size variation and their measurement in natural populations

Measurement of intrapopulation variation in secondary sexual traits is a priority in the testing of sexual selection models. However, it is important to take care in the choice of materials and delimitation of populations. The use of museum skins to study variation in male tail ornaments may substantially underrepresent the real degree of intrapopulation variation. Data from live animals in specific areas provide more realistic estimates, and should be used whenever possible. I use as an example field data on male ornament length and body size in Vidua macroura (Aves: Ploceidae), a promiscuous, parasitic African finch with elongated tail plumes. Individual males differ in the timing and rate of ornament growth, and females are therefore faced with a large degree of phenotypic variation in male ornament size, even though genetic variation may not be great. By correcting for seasonal variation in the ornament lengths of males caught at different times, I show that mid-season coefficients of variation in ornament length of breeding males in two populations are as high as 18% and 55%. By contrast, tarsus, wing and unornamented tail lengths of the same males vary from 2 to 4%.     

Maximum body size among insular Komodo dragon populations covaries with large prey density

This study documents variation in maximum body size of Komodo dragons ( Varanus komodoensis ) among the four extant island populations in Komodo National Park and compares an indirect measure of deer density, the major prey item for large dragons, to differences in maximum body size among islands. The largest 15% of dragons from the large islands of Komodo and Rinca were significantly longer and heavier than the largest 15% of dragons on the small islands of Gili Motang and Nusa Kode. There was a 33% difference in snout vent length (SVL) between dragons found on Komodo and those found on Gili Motang, with mass varying by more than four-fold. Density of deer pellet groups between islands ranged from 5.86±0.75 groups per transect on Gili Motang to 20.73±1.02 groups per transect on Komodo Island. Maximal dragon SVL and mass was highly positively correlated with this index of deer density. Low prey density on the two small islands could constrain body size via energetic constraints. At present we can not deduce if insular body size variation has arisen through genotypic or phenotypic mechanisms.     

The power of the seasons: rainfall triggers parental care in poison frogs

The quality of breeding sites is of great importance for the reproductive success and accordingly the fitness of many animal species. Hence, individuals should decide carefully where to rear their offspring. Often parents have to account for multiple characteristics of habitat quality at once, which in turn might change over time. Specimens confronted with such variability may evolve the ability to display context-dependant decision plasticity. Anuran amphibians breeding in ephemeral pools largely face two risks for their offspring: desiccation and predation. The Neotropical poison frog Ranitomeya variabilis deposits both eggs and tadpoles in phytotelmata. These small tadpole nurseries lower the risk of offspring predation. However, because most poison frog tadpoles are cannibalistic, even these pools need to be surveyed for predators, and parents tend to avoid deposition with conspecifics. We tested if this avoidance behaviour does change in parental R. variabilis depending on seasonal circumstances. Over several months we provided the frogs the option to deposit their eggs or tadpoles in pools that did and did not contain chemical cues of cannibalistic conspecifics, respectively. During the rainy season, frogs strongly avoided conspecific cues for both eggs and tadpoles. Anyway, with the change to the dry season, parental preferences changed such that parent frogs were more likely to deposit tadpoles (but not eggs) in pools containing cues of conspecific tadpoles. We suggest that R. variabilis, a species that typically isolates its cannibalistic offspring, has evolved a plastic feeding behaviour with regard to the risk of phytotelmata desiccation. We interpret that parents provide older tadpoles with younger ‘trophic’ tadpoles in order to accelerate their development and save them from impending desiccation.