Clutch size versus clutch interval: life history strategies in the colour-polymorphic pygmy grasshopper Tetrix subulata

Theory posits that reproduction carries a cost in terms either of future fecundity, growth or survival. Different life history strategies may evolve in response to different external sources of mortality. In ectothermic organisms, such as insects and reptiles, reproductive characteristics may also vary due to effects of differences in body temperature on activity and physiological performance. In this study, female pygmy grasshoppers [Tetrix subulata (L.) Orthoptera: Tetrigidae] belonging to four different colour morphs were maintained under two different temperatures, and data on reproductive life history traits were used to test for costs of reproduction, plasticity of reproductive characteristics in response to temperature and variation among colour morphs in reproductive strategies. The results revealed that average clutch size decreased progressively from the first to third clutch, and that females producing relatively large clutches displayed a greater reduction (in both absolute and relative terms) in the number of eggs to the following clutch, as expected from the hypothesis that present reproduction negatively affects future fecundity. Great expenditure on present reproduction also negatively influenced the time to next clutch:the decrease in mean clutch size with clutch number was associated with a reduction in inter-clutch interval, and clutch interval increased with clutch size across individuals within colour morphs. Females maintained in a warm environment were more likely to oviposit, laid their first clutch earlier, produced more clutches and had shorter intervals between sequential clutchesthan females in a cold environment, suggesting that differences in body temperature may contribute to variation in reproductive performance within and among natural populations. A comparison among colour morphs maintained under identical conditions suggested that females belonging to certain morphs produce relatively large clutches at the expense of fewer clutches per unit time. However, experimental data revealed no difference in relative fat content between dark and pale individuals maintained either in sun-exposed outdoor enclosures (where they were unable to increase their body temperature by basking) or in shaded enclosures. This suggest that the divergence in life history strategies among colour morphs may reflect a response to morph-specific differences in adult survival imposed by visually searching predators, rather than being due to the effects of differences in body temperature.     

Reproductive life history variation among colour morphs of the pygmy grasshopper Tetrix subulata

Individuals of pygmy grasshoppers ( Tetrix subulata [L.] Orthoptera: Tetrigidae) exhibit genetically coded discontinuous variation in colour pattern. To determine whether reproductive performance is likely to be affected by colour pattern, this study investigated variation in body size and reproductive life-history characteristics among individuals belonging to five different colour morphs. The proportion of reproductive females (i.e. females with eggs) declined significantly as the season progressed (from 100% in mid-May to 40% in mid-June), but no such seasonal trend was apparent for body size, clutch size or egg size. Colour morphs differed significantly in body size, and these size differences accounted for most of the variation in clutch size and egg size. Colour morphs also differed in the regression of egg size on clutch size, suggesting that trade-offs between number and size of offspring might vary among morphs. Finally, I found a negative relationship across colour morphs between the proportion of females with eggs and average clutch size. This suggests that individuals belonging to certain colour morphs produce a relatively large number of clutches per unit time, at the expense of fewer offspring in each clutch, compared to other morphs. Collectively, my results indicate that different colour morphs of T. subulata may have different reproductive strategies. These differences may reflect variation in thermoregulatory capacity or differences in probability of survival induced by visual predators.     

Variation in thermal sensitivity of performance among colour morphs of a pygmy grasshopper

Populations of pygmy grasshoppers, Tetrix subulata, display genetically coded discrete variation in colour pattern and there are differences among morphs in the capacity to achieve body heating. To determine whether colour morphs differ in thermal physiology, I assessed reaction distance and jumping performance of individuals belonging to different morphs at two different temperatures. Individuals allowed a potential predator to approach less closely and jumped longer distances at high than at low temperature. My analyses also uncovered variation among morphs in average reaction distance and jumping capacity, as well as in thermal sensitivity of these two traits. Matrix correlation analysis further revealed that pair-wise differences between morphs in thermal sensitivity of jumping performance (but not reaction distance) could be accurately predicted by differences in body temperatures preferred in a laboratory thermal gradient. These results support the view that morphology, behaviour and thermal physiology of ectotherms may evolve in concert. The relationship between reaction distance and jumping performance varied among colour morphs at high temperature, and the common within-morph relationship between these two traits deviated from the corresponding among-morph relationship. This suggests that the variation among morphs has partially arisen through active divergence, with selection having influenced both traits and modifications having occurred to different degrees in different morphs. My data further suggest that pale colour morphs, with a limited capacity to attain high body temperatures, may not necessarily be at a selective disadvantage, because their physiology may be adapted to lower body temperatures.     

Developmental instability and immune function in colour polymorphic pygmy grasshoppers

Random left minus right deviations from symmetry in otherwise bilaterally symmetric traits may arise due to developmental instability in response to environmental stress. Here we test for variation in developmental instability, measured as asymmetry of (femur) size, among individuals belonging to four different genetically encoded colour morphs of the pygmy grasshopper Tetrix undulata (Sow.) (Orthoptera: Tetrigidae). Such a difference is expected under the hypotheses that perturbed growth and development and concomitant morphological asymmetry may result from exposure to unfavourable temperatures or costs associated with melanization, or reflect a by-product of past disease in individuals with poor immune responsiveness. Results from mixed model two-way ANOVAs uncovered no statistically significant directional asymmetry in femur size, whereas non-directional asymmetry was significant in each of the four different colour morphs. The degree of intraindividual, interlateral variance in femur size varied significantly among individuals belonging to different colour morphs, being considerably higher in the black morph, which also suffers the greatest risk of overheating, compared to the brown, striped and grey morphs. Asymmetry in femur size was not associated with one measure of immune responsiveness, the encapsulation response of individuals experimentally implanted with a novel antigen consisting of a nylon mono-filament. These results are consistent with the notion that individual pigmentation pattern may indirectly influence developmental instability and morphological asymmetry, via the effects of coloration on body temperature.Co-ordinating editor: Hurst     

Coevolution of color pattern and thermoregulatory behavior in polymorphic pygmy grasshoppers Tetrix undulata

Ectothermic organisms, such as insects and reptiles, rely on external heat sources to control body temperature and possess physiological and behavioral traits that are temperature dependent. It has therefore been hypothesised that differences in body temperature resulting from phenotypic properties, such as color pattern, may translate into selection against thermally inferior phenotypes. We tested for costs and benefits of pale versus dark coloration by comparing the behaviors (i.e., basking duration and bouts) of pygmy grasshopper (Tetrix undulata) individuals exposed to experimental situations imposing a trade-off between temperature regulation and feeding. We used pairs consisting of two full-siblings of the same sex that represented different (genetically coded) color morphs but had shared identical conditions from the time of fertilization. Our results revealed significant differences in behavioral thermoregulation between dark and pale individuals in females, but not in males. Pale females spent more time feeding than dark females, regardless of whether feeding was associated with a risk of either hypothermia or overheating. In contrast, only minor differences in behavior (if any) were evident between individuals that belonged to the same color morph but had been painted black or gray to increase and decrease their heating rates. This suggests that the behavioral differences between individuals belonging to different color morphs are genetically determined, rather than simply reflecting a response to different heating rates. To test for effects of acclimation on behaviors, we used pairs of individuals that had been reared from hatchlings to adults under controlled conditions in either low or high temperature. The thermal regime experienced during rearing had little effect on behaviors during the experiments reported above, but significantly influenced the body temperatures selected in a laboratory thermal gradient. In females (but not in males) preferred body temperature also varied among individuals born to mothers belonging to different color morphs, suggesting that a genetic correlation exists between color pattern and temperature preferences. Collectively, these findings, at least in females, are consistent with the hypothesis of multiple-trait coevolution and suggest that the different color morphs represent alternative evolutionary strategies.     

Some like it hot: Intra-Population Variation in behavioral Thermoregulation in Color-Polymorphic pygmy Grasshoppers

Ectothermic animals rely on external heat sources and behavioral thermoregulation to control body temperature, and are characterized by possessing physiological and behavioural traits which are temperature dependent. It has therefore been suggested that constraints on the range of body temperatures available to individuals imposed by phenotypic properties, such as coloration, may translate into differential fitness and selection against thermally inferior phenotypes. In this paper, I report an association between thermal preferences and thermal capacity (the ability to warm up when insolated) across different genetically coded color morphs of the pygmy grasshopper Tetrix subulata. Data on behavioral thermoregulation of individuals in a laboratory thermal gradient revealed a preference for higher body temperatures in females than in males, and significant variation among colour morphs in preferred body temperatures in females, but not in males. The variation in females was in perfect accordance with estimates of morph-specific differences in thermal capacity. Thus, dark morphs not only attain higher temperatures when exposed to augmented illumination, but also prefer higher body temperatures, compared to paler morphs. This intra-population divergence probably reflects an underlying variation among colour morphs in temperature optima, and is consistent with the notion that coloration, behaviour and physiology evolve in concert.     

Oxygen consumption in offspring tawny owls Strix aluco is associated with colour morph of foster mother

In several colour polymorphic species, morphs differ in thermoregulation either because dark and pale surfaces absorb solar radiation to a different extent and/or because morphs differ in key metabolic processes. Morph-specific thermoregulation may potentially account for the observation that differently coloured individuals are frequently not randomly distributed among habitats, and differ in many respects, including behaviour, morphology, survival and reproductive success. In a wild population of the colour polymorphic tawny owl Strix aluco, a recent cross-fostering experiment showed that offspring raised and born from red mothers were heavier than those from grey mothers. In the present study, we tested in the same individuals whether these morph-specific offspring growth patterns were associated with a difference in metabolic rate between offspring of red and grey mothers. For this purpose, we measured nestling oxygen consumption under two different temperatures (laboratory measurements: 4 and 20°C), and examined the relationships between these data sets and the colour morph of foster and biological mothers. After controlling for nestling body mass, oxygen consumption at 20°C was greater in foster offspring raised by grey foster mothers. No relationship was found between nestling oxygen consumption and coloration of their biological mother. Therefore, our study indicates that in our experiment offspring raised by grey foster mothers showed not only a lower body mass than offspring raised by red foster mothers, but also consumed more oxygen under warm temperature. This further indicates that rearing conditions in nests of grey mothers were more stressful than in nests of red mothers.     

Immune function, parasitization and extended phenotypes in colour polymorphic pygmy grasshoppers

Ecological and evolutionary consequences of host–parasite interactions have attracted considerable attention from evolutionary biologists. Previous studies have suggested that immune responsiveness may be genetically or developmentally linked with colour pattern, such that the evolution of animal colour patterns may be influenced by correlated responses to selection for parasite resistance. We studied interactions between the endoparasitic fly Leiophora innoxia (Meigen) (Diptera: Tachinidae) and its colour polymorphic pygmy grasshopper host Tetrix undulata (Sow.) (Orthoptera: Tetrigidae) to test for morph‐specific differences in parasitization and immune defence, and host‐induced variation in parasite phenotypes. Our results revealed that c. 2 and 30% of adult grasshoppers collected from the same natural population in two subsequent years, respectively were parasitized. Parasite prevalence was independent of host sex and colour morph. Pupae were larger if the parasite had developed in a female than in a male host, possibly reflecting host resource value or a physical constraint on larval growth imposed by host body size. Pupal size was also associated with host colour morph, with individuals that had developed in dark morphs being smaller at pupation compared to those that developed in paler morphs. However, immune defence, measured as the encapsulation response to a novel antigen, did not differ among individuals belonging to alternative colour morphs or sexes. Darker morphs warm up more quickly and prefer higher body temperatures than paler ones. Encapsulation was not influenced by maintenance temperature (15 vs. 30 °C), however, suggesting that indirect effects of coloration on parasite resistance mediated via differential body temperature are unlikely. The dependence of parasite body size on host colour morph may thus reflect plasticity of growth and development of the larvae in response to differential host body temperature, rather than variable host immune defence. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 373–383.     

Body size influences differently the detectabilities of colour morphs of cryptic prey

Body size and coloration may contribute to variation in performance and fitness among individuals; for example, by influencing vulnerability to predators. Yet, the combined effect of size and colour pattern on susceptibility to visual predators has received little attention, particularly in camouflaged prey. In the colour polymorphic pygmy grasshopper Tetrix subulata (Linnaeus, 1758), females are larger than males, although there is a size overlap between sexes. In the present study, we investigated how body size and colour morph influenced detection of these grasshoppers, and whether differences in protective value among morphs change with size. We conducted a computer‐based experiment and compared how human ‘predators’ detected images of large, intermediate or small grasshoppers belonging to black, grey or striped colour morphs when embedded in photographs of natural grasshopper habitats. We found that time to detection increased with decreasing size, that differences in time to detection of the black, grey and striped morphs depended differently on body size, and that no single morph provided superior or inferior protection in all three size classes. By comparing morph frequencies in samples of male and female grasshoppers from natural populations, we also examined whether the joint effects of size and colour morph on detection could explain evolutionary dynamics in the wild. Morph frequency differences between sexes were largely in accordance with expectations from the results of the detection experiment. The results of the present study demonstrate that body size and colour morph can interactively influence detection of camouflaged prey. This may contribute to the morph frequency differences between male and female pygmy grasshoppers in the wild. Such interactive effects may also influence the dynamics of colour polymorphisms, and contribute to the evolution of ontogenetic colour change and sexual dichromatism. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 112–122.     

Effects of phenotypic variation onto body temperature and flight activity in a polymorphic insect

Abstract.  According to biophysical principles, colour and size are important phenotypic factors that may influence body temperature and activity in ectothermic insects. In taxa showing female-limited polymorphism, males and female morphs differ in body colour, size and activity pattern. However, no previous study has evaluated whether such phenotypic and behavioural variation relates to differences between males and female morphs in thermal properties. In the present study, the relationships between body colour, size, activity and body temperature are examined under laboratory and field conditions, for the polymorphic damselfly Enallagma cyathigerum (Charpentier, 1840) (Odonata: Zygoptera). Contrary to expectation, males and female colour morphs of this species do not differ in thermal properties (i.e. heating characteristics or field body temperatures). When questioning phenotype and activity, temperature does not appear to be relevant for understanding the maintenance of female-limited polymorphism.     

Determinants of survival in juvenile Psammodromus algirus lizards

Theories posit that the relative mortality rate of adults and juveniles is a major determinant of population dynamics and life history evolution. Moreover, differential survival of pre-reproductive individuals may be an important source of variation in lifetime reproductive success, and characters that influence survival of juveniles are likely to be under strong selection. We examined survival from hatching to maturity in a natural population of Psammodromus algirus lizards using data from a capture-mark-recapture study. We found that mortality from hatching to maturity was high: only 8% of males and 14% of females that hatched in 1996 survived the entire study period until maturity in spring 1998. The probability of survival was 75% during both the first and second overwinter periods when lizards were inactive most of the time, and about 25% during their first spring to autumn activity season. Our analyses further revealed significant associations between survival and snout-vent length, body condition, sex and microhabitat use. However, the relationship between survival and morphological characters varied among time periods, presumably because the sources of mortality during the activity season were different from those during hibernation. The association between survival and body condition also varied within time periods, both between large and small individuals and between the two sexes. This suggests that the relative importance of different selective agents may change during the life of individuals and vary between males and females due to differences in body size and behaviour. Received: 24 March 1999 / Accepted: 14 February 2000     

Rethinking the thermal melanism hypothesis: rearing temperature and coloration in pygmy grasshoppers

Selection for efficient conversion of solar radiation to body heat has favored the evolution of dark coloration in many ectotherms. The thermal melanism hypothesis posits that dark coloration is beneficial under conditions of low ambient temperatures because it results in faster heating rates and higher body temperatures. Fast heating rates, however, may come at a cost of overheating unless compensated for by thermal physiology or behaviour. Pygmy grasshopper (Orthoptera, Tetrigidae) populations that inhabit fire-ravaged areas characterized by blackened backgrounds and hot surface temperatures due to high absorbance of solar radiation show an increased frequency of black phenotypes. I raised the progeny of wild-captured Tetrix undulata in cold and hot temperatures and used data on color patterns and survival in a greenhouse to examine whether a cold thermal environment triggered the development of melanic coloration or differently affected survival of melanic versus non-melanic individuals. My results indicate that melanism was not influenced by rearing temperature but by genes or epigenetic maternal effects. Temperature also did not affect survival. However, melanic individuals produced by melanic mothers survived longer than melanic individuals produced by non- melanic mothers, whereas non-melanic individuals produced by non-black mothers survived longer than melanic individuals produced by non-black mothers. This suggests a mismatch between color and physiology in offspring belonging to a different color morph than their mother. Future investigations into the evolution of melanism should consider conflicting selection pressures on thermal capacity and camouflage as well as the influence of correlated responses to selection on traits associated with coloration.     

Opposing fitness consequences of colour pattern in male and female snakes

Local populations of the adder, Vipera berus, are polymorphic for dorsal colour pattern, containing both melanistic (black) and zig-zag patterned individuals. Colour patterns in snakes influence crypsis and thermoregulatory capacity and therefore may be subjected to natural selection. To find an explanation for the maintenance of this polymorphism I examined temporal and spatial variation in morph frequency, and tested for differential selection among morphs using data from a six year capture-mark-recapture study. The data derive from six groups of islands in the Baltic Sea off the Swedish east coast, two mainland localities near the coast, and one inland locality. Morph frequency did not change over time within a population but varied among populations: melanistic individuals were not found at the inland locality, but comprised from 17 to 62% of the coastal and island populations. Adders frequently moved between islands within a group, but the tendency to disperse was independent of morph. These results suggest that the polymorphism is stable and maintained by a deterministic process. Scar frequency was twice as high among melanistic as among zig-zag snakes, and melanistic individuals were easier to capture, indicating that predation may be higher on the melanistic morph. Colour morphs did not differ in body size, but analysis of recapture data shows evidence for differential survival among morphs. Zig-zag males survived better than melanistic males, but the relative survival rates of morphs were reversed in females. This difference was consistent through time and may be due to sexual differences in behaviour, with melanism increasing predation intensity when associated with male but not with female behaviour. Opposing fitness consequences of colour pattern in the two sexes may help maintain colour polymorphism within populations of Vipera berus.     

Inherited differences in head allometry in polymorphic Arctic charr from Loch Rannoch, Scotland

Planktivorous and benthivorous morphs of wild Arctic charr Salelinus alpinus from Loch Rannoch, Perthshire, Scotland, reared in the laboratory from artificially fertilized eggs under identical conditions, were morphologically distinct (based on a series of head measurements) from an early age. For some morphometric characters, these differences became more marked with increasing body size, reflecting differences in the allometric growth patterns of the two forms. These data show that the observed phenotypic differences between these two trophic variants were, to some extent at least, inherited. Thus it is concluded that the mechanisms regulating expression of phenotype in the sympatric morphs of Loch Rannoch are significantly different from the environmentally determined body size polymorphisms reported from Norway but are closer to the more completely divergent forms from Thingvalavatn, Iceland.     

Effects of temperature on the expression of elytral colour polymorphism in the ladybird beetle,Menochilus sexmaculatus (Coleoptera: Coccinellidae)

The ladybird beetle, Menochilus sexmaculatus (Fabricius), has a remarkable elytral colour polymorphism composed of black and red. In the present study, we investigated the effect of temperature on growth from the first instar larva to the pupal stage, as well as maternal morph types on the phenotypic expression of the elytral colour morph in a polymorphic population from Osaka, Japan. Female individuals of three different elytral colour morphs were collected from a wild population, and hatchlings from each female were divided into three groups, which were reared at three constant temperatures: 20 °C, 25 °C, and 30 °C. The phenotypic frequency of F₁ adults indicated that the elytral morph type was determined by genetic factors, but not by growth temperatures. Namely, type A (almost black morph) was the most abundant in F₁ from type A mothers (Male: 52.6%; Female: 32.3%); and types B (four small-dotted morph) and F (four medium-dotted morph) were the most abundant from type B (Male: 56.7%; Female: 53.3%) and type G (four larger-dotted morph) mothers (Male: 33.3%; Female: 31.3%), respectively. Therefore, the expression of elytral colour polymorphism in the Osaka, Japan population is likely to have a genetic basis contingent on parental morphs, rather than a phenotypic plasticity associated with growth temperatures.     

Why get big in the cold? Size–fecundity relationships explain the temperature‐size rule in a pulmonate snail (Physa)

Most ectotherms follow a pattern of size plasticity known as the temperature‐size rule where individuals reared in cold environments are larger at maturation than those reared in warm environments. This pattern seems maladaptive because growth is slower in the cold so it takes longer to reach a large size. However, it may be adaptive if reaching a large size has a greater benefit in a cold than in a warm environment such as when size‐dependent mortality or size‐dependent fecundity depends on temperature. I present a theoretical model showing how a correlation between temperature and the size–fecundity relationship affects optimal size at maturation. I parameterize the model using data from a freshwater pulmonate snail from the genus Physa. Nine families were reared from hatching in one of three temperature regimes (daytime temperature of 22, 25 or 28 °C, night‐time temperature of 22 °C, under a 12L : 12D light cycle). Eight of the nine families followed the temperature‐size rule indicating genetic variation for this plasticity. As predicted, the size–fecundity relationship depended upon temperature; fecundity increases steeply with size in the coldest treatment, less steeply in the intermediate treatment, and shows no relationship with size in the warmest treatment. Thus, following the temperature‐size rule is adaptive for this species. Although rarely measured under multiple conditions, size–fecundity relationships seem to be sensitive to a number of environmental conditions in addition to temperature including local productivity, competition and predation. If this form of plasticity is as widespread as it appears to be, this model shows that such plasticity has the potential to greatly modify current life‐history theory.     

The adaptive significance of colour pattern polymorphism in the Australian scincid lizard Lampropholis delicata

Females of Lampropholis delicata are dimorphic for colour pattern, the difference between morphs being the presence or absence of a distinct white mid-lateral stripe. A less distinct striped morph occurs also in males. We evaluated alternative hypotheses for the maintenance of this polymorphism by examining temporal and spatial variation in morph frequency, testing for differential selection among morphs using data on body size and reproductive traits from preserved specimens, and experimentally manipulating colour pattern in free-ranging lizards of both sexes, to assess the influence of the lateral stripe on survival rates. We found that the relative frequency of striped individuals varied among populations and decreased from north to south in both sexes, coincident with an increasing incidence of regenerated tails. Morph frequencies did not change through time within a population. Striped gravid females appeared to survive better and produced larger clutches than did non-striped females. In our experimental study, the relationship between survival and colour morph differed between the two sexes; males painted with a white lateral stripe had lower survival than control (brown stripe) males, but survival did not differ between striped and control females. The different response in the two sexes may be due partly to differences in temperature and microhabitat selection. We propose that the white lateral stripe decreases susceptibility to predators in gravid females but increases risk of predation in males, especially in combination with low temperatures. The polymorphism might be maintained by: (1) opposing fitness consequences of the stripe in males and females; (2) sex-specific habitat selection; and (3) gene flow in combination with spatial variation in relative fitness of the two morphs.     

The effect of a seasonal time constraint on development time, body size, condition, and morph determination in the horned beetle Allomyrina dichotoma L. (Coleoptera: Scarabaeidae)

Abstract.  1. In horned beetles selection favours males that adjust their investment in horn development in relation to cues that predict adult body size. Here it is shown that in the Japanese horned beetle, Allomyrina dichotoma . There is a significant discontinuity in the horn length body size allometry. This can be described as a linear relationship that is shifted towards an increased horn length to body length ratio in males with horns longer than 16 mm.
2. Larval nutrition explains morph determination in A. dichotoma . However, unlike other species, variation in larval nutrition was the result of a seasonal time constraint that limits the time available for feeding prior to the onset of winter diapause.
3. Even when eggs were reared with an ad libitum food supply, minor morphs were still observed. Individuals that were oviposited later in the season had less time to feed, shorter development times, eclosed as smaller individuals and, in the case of males, were more likely to be hornless. Major morphs, minor morphs, and females all reduced their body size in response to seasonal time constraints in the same way. However, males that were laid later in the season had faster development times than females laid at the same time, but showed no reduction in their size relative to females, suggesting seasonal time constraints increase growth rates in males but not in females.
4. No evidence was found that seasonal time constraints resulted in a reduction of size-corrected fat reserves at eclosion, or that minor morphs gained any developmental advantage by reducing investment in horn length.     

Experimental manipulation reveals differential effects of colour pattern on survival in male and female pygmy grasshoppers

Populations of pygmy grasshoppers, Tetrix subulata, exhibit genetically coded discontinuous variation in colour pattern. To determine whether the dynamics of this polymorphism is likely to be affected by selective processes, rather than by stochastic events, we experimentally manipulated colour patterns of free-ranging grasshoppers and then calculated and controlled for differences in capture probabilities between categories of individuals before estimating and testing for differences in survival using mark–recapture data and program SURGE . We found that paint treatment had a significant effect on survival, and that the relationship between colour pattern and survival was different in males and females. Our analyses also revealed significant differences between sexes in relative frequencies of natural colour morphs, body size, activity pattern, dispersal distance and microhabitat use. These findings accord with the hypothesis that colour pattern and behaviour jointly determine susceptibility to visual predators. Our data enable us to reject the null-hypothesis that colour pattern is a selectively neutral character and that the polymorphism is maintained solely by stochastic processes, such as random genetic drift and founder events. Indeed, the effect of dorsal coloration on survival, together with associations between colour pattern and many biologically important traits (body size, behaviour, thermal capacity, physiology and reproductive performance), suggests that colour pattern is likely to significantly influence individual fitness, and that the polymorphism must be maintained by some active process, such as spatially variable selection in combination with gene flow. The possible role of colour polymorphism as an intermediate stage in the evolution of sexual dichromatism in animals is discussed.     

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.