[Show abstract][Hide abstract] ABSTRACT: In many incubating birds heat transfer from parent to egg is facilitated by the brood patch, an area of ventral abdominal skin that becomes highly vascularised, swells and loses its down feathers around the time of laying. Only the female develops a brood patch in most passerine species, but some males incubate and maintain the eggs at similar temperatures to females without a brood patch. Here we used a novel application of infra-red thermography (IRT) to examine sex differences in parental care from a physiological perspective. Using incubating male and female zebra finches (Taeniopygia guttata), a species in which the male lacks a brood patch, we measured the surface temperature of the ventral plumage overlying the abdomen and a reference area that does not contact the eggs (thorax) twice per pair. In half of the pairs clutch size was experimentally enlarged between the two sets of measurements to increase incubation demand. We found that the temperature differential between abdomen and thorax plumage was greater in females than in males, and that abdomen plumage was warmer after clutch enlargement than before it in females but not in males. These findings are consistent with morphological sex differences in brood patch development and suggest that male and female zebra finches differ in the way they regulate abdomen versus general body surface temperature in response to variation in incubation demand.
Full-text · Article · Dec 2013 · Journal of Experimental Biology
[Show abstract][Hide abstract] ABSTRACT: Whether parental effort can be negotiated between partners over ecological time and adjusted across different contexts is
not well understood. We manipulated male extra-pair copulation (EPC) opportunity in captive zebra finches, Taeniopygia guttata, to test whether males adjust incubation effort to the mating context and to examine how females respond to their partner’s
effort. Birds without previous breeding experience were paired randomly and bred with the same partner twice. In the first
breeding attempt, half the males received EPC opportunities with ‘extra-pair females’ during incubation, while the other half
did not. Males that received EPC opportunities in the first breeding attempt did not in the second breeding attempt and vice
versa. We recorded incubation effort on days when EPC opportunities were not presented. In their first breeding attempt, males
with EPC opportunities incubated less than those without. Females compensated fully for the deficit in male care so that a
pair’s combined incubation effort was unchanged. In the second attempt, when a male’s opportunity for EPCs was switched, individuals
showed the same level of incubation effort that they had previously, irrespective of the current availability of extra-pair
females. This suggests that division of effort was negotiated in the first breeding attempt and maintained without significant
adjustments in the second attempt. The effects of male EPC opportunity in the first breeding attempt on subsequent incubation
effort suggests that individual parental decisions can be shaped by previous experience and this may partly explain conflicting
results in studies where individuals’ histories were not known.
KeywordsClutch size–Compensation–EPC–Incubation–Sealed bid–
No preview · Article · Nov 2011 · Behavioral Ecology and Sociobiology
[Show abstract][Hide abstract] ABSTRACT: 1. Carotenoid-based signals typically vary in both the total concentration of carotenoids deposited and the relative quantities of different constituent carotenoids. As these constituents often have differing spectral properties, the relative and absolute concentrations of different carotenoids deposited in a signal can significantly affect the spectrum of light reflected. A critical but rarely tested assumption of hypotheses concerning the information content of carotenoid-based signals is that their colour directly reveals the concentration and composition of constituent carotenoids to intended recipients. Most previous studies have attempted to address this question using either photographic techniques or by analysing recorded reflectance spectra, neither of which take into account the specific properties of the receiver’s visual system.
2. Here, we use psychophysical models of the visual system of three-spined sticklebacks (Gasterosteus aculeatus) to estimate their sensitivity to variation in the concentration and relative abundance of constituent carotenoids of males’ carotenoid-based sexual signals.
3. We demonstrate that sticklebacks are acutely sensitive to variation in both the total concentration of carotenoids in the signal and the relative proportion of its constituents, and that the accuracy of these assessments is largely unaffected by the presence or absence of ultraviolet radiation in the illuminant. We discuss these findings in relation to the evolution, maintenance and information content of carotenoid-based sexual signals.
Full-text · Article · Nov 2010 · Functional Ecology
[Show abstract][Hide abstract] ABSTRACT: A mechanism commonly suggested to explain the persistence of color polymorphisms in animals is negative frequency-dependent selection. It could result from a social dominance advantage to rare morphs. We tested for this in males of red and blue color morphs of the Lake Victoria cichlid, Pundamilia. Earlier work has shown that males preferentially attack the males of their own morph, while red males are more likely to win dyadic contests with blue males. In order to study the potential contribution of both factors to the morph co-existence, we manipulated the proportion of red and blue males in experimental assemblages and studied its effect on social dominance. We then tried to disentangle the effects of the own-morph attack bias and social dominance of red using simulations. In the experiment, we found that red males were indeed socially dominant to the blue ones, but only when rare. However, blue males were not socially dominant when rare. The simulation results suggest that an own-morph attack bias reduces the social dominance of red males when they are more abundant. Thus, there is no evidence of symmetric negative frequency-dependent selection acting on social dominance, suggesting that additional fitness costs to the red morph must explain their co-existence.
[Show abstract][Hide abstract] ABSTRACT: Elevated breeding effort is known to increase an individual's rate of senescence, although the underlying mechanisms are not well understood. One possibility is that the ability to resist senescence is limited by the availability of antioxidants, which are necessary to mitigate the deleterious effects of oxidative stress thought to underlie the aging process. Susceptibility to oxidative stress is likely to be particularly high during reproduction, and so for a given level of reproductive effort, the rate of senescence should be fastest in those individuals with the poorest antioxidant capacity. We tested this hypothesis in an experimental study of breeding male three-spined sticklebacks (Gasterosteus aculeatus) held under a high or low reproduction regime and fed on either high or low levels of carotenoids (potentially limiting dietary compounds with antioxidant properties). Fish on the high reproduction regime and those on the low-carotenoid diet both showed an accelerated decline in sustained swimming performance (an indicator of locomotor senescence) compared with males on the low reproduction regime and high-carotenoid diet, respectively. The swimming performance of fish subjected to the high rate of reproduction, but fed a low-carotenoid diet, appeared to decline most rapidly, perhaps because of the additive effects of increased levels of reproduction-induced oxidative stress and lower antioxidant availability. These findings show that both dietary carotenoid intake and breeding effort can impact on the age-related decline in swimming performance and have important implications for female choice and the capacity of males with insufficient antioxidant defenses to adequately perform paternal care. Copyright 2010, Oxford University Press.
Full-text · Article · Aug 2010 · Behavioral Ecology
[Show abstract][Hide abstract] ABSTRACT: Sexual selection acting on male traits through female mate choice is commonly inferred from female association preferences
in dichotomous mate choice experiments. However, there are surprisingly few empirical demonstrations that such association
preferences predict the likelihood of females reproducing with a particular male. This information is essential to confirm
association preferences as good predictors of mate choice. We used green swordtails (Xiphophorus helleri) to test whether association preferences predict the likelihood of a female reproducing with a male. Females were tested
for a preference for long- or short-sworded males in a standard dichotomous choice experiment and then allowed free access
to either their preferred or non-preferred male. If females subsequently failed to produce fry, they were provided a second
unfamiliar male with similar sword length to the first male. Females were more likely to reproduce with preferred than non-preferred
males, but for those that reproduced, neither the status (preferred/non-preferred) nor the sword length (long/short) of the
male had an effect on brood size or relative investment in growth by the female. There was no overall preference based on
sword length in this study, but male sword length did affect likelihood of reproduction, with females more likely to reproduce
with long- than short-sworded males (independent of preference for such males in earlier choice tests). These results suggest
that female association preferences are good indicators of female mate choice but that ornament characteristics of the male
are also important.
Full-text · Article · Mar 2010 · Behavioral Ecology and Sociobiology
[Show abstract][Hide abstract] ABSTRACT: It has been suggested that Plethodontid salamanders are excellent candidates for indicating ecosystem health. However, detailed, long-term data sets of their populations are rare, limiting our understanding of the demographic processes underlying their population fluctuations. Here we present a demographic analysis based on a 1996-2008 data set on an underground population of Speleomantes strinatii (Aellen) in NW Italy. We utilised a Bayesian state-space approach allowing us to parameterise a stage-structured Lefkovitch model. We used all the available population data from annual temporary removal experiments to provide us with the baseline data on the numbers of juveniles, subadults and adult males and females present at any given time.
Sampling the posterior chains of the converged state-space model gives us the likelihood distributions of the state-specific demographic rates and the associated uncertainty of these estimates. Analysing the resulting parameterised Lefkovitch matrices shows that the population growth is very close to 1, and that at population equilibrium we expect half of the individuals present to be adults of reproductive age which is what we also observe in the data. Elasticity analysis shows that adult survival is the key determinant for population growth.
This analysis demonstrates how an understanding of population demography can be gained from structured population data even in a case where following marked individuals over their whole lifespan is not practical.
[Show abstract][Hide abstract] ABSTRACT: Using a threshold-triggering framework, we extend the Moran effect to also cover timing of life history events. With two varieties
of the model we demonstrate emergence of synchrony in seasonal and annual timing that levels off against distance between
sampling sites compared. In the first model we address within-season timing over years. The Finnish data on leafing of European
aspen support the model predictions in al detail explored. In the second example the focus is on annual match of seed production
in the Finnish Scotch pine and Norway spruce. The model predictions find their match with the data. We show that it is possible
to extend Moran’s (1953) idea to encompass events not directly regulated by density-dependent feedback. It is perhaps not
too surprising that phenological events can be synchronized in much the same way as population fluctuations.
KeywordsLife history-Phenology-Spatial synchrony-The Moran effect-Threshold-triggering
[Show abstract][Hide abstract] ABSTRACT: In species where males express carotenoid-based sexual signals, more intensely coloured males may be signalling their enhanced ability to combat oxidative stress. This may include mitigating deleterious oxidative damage to their sperm, and so be directly related to their functional fertility. Using a split-clutch in vitro fertilization technique and dietary carotenoid manipulation, we demonstrate that in non-competitive fertilization assays, male three-spined sticklebacks (Gasterosteus aculeatus) that are fed higher (but biologically relevant) levels of carotenoids had a significantly increased fertilization success, irrespective of maternal carotenoid intake. Furthermore, within diet groups, a male's fertilization success was positively related to the expression of his carotenoid-based nuptial coloration, with more intensely coloured males having higher functional fertility. These data provide, to our knowledge, the first demonstration that dietary access to carotenoids influences fertilization success, and suggest that females could use a male's nuptial coloration as an indicator of his functional fertility.
[Show abstract][Hide abstract] ABSTRACT: In species in which males are free to dynamically alter their allocation to sexual signaling over the breeding season, the optimal investment in signaling should depend on both a male's state and the level of competition he faces at any given time. We developed a dynamic optimization model within a game-theoretical framework to explore the resulting signaling dynamics at both individual and population levels and tested two key model predictions with empirical data on three-spined stickleback (Gasterosteus aculeatus) males subjected to dietary manipulation (carotenoid availability): (1) fish in better nutritional condition should be able to maintain their signal for longer over the breeding season, resulting in an increasingly positive correlation between nutritional status and signal (i.e., increasing signal honesty), and (2) female preference for more ornamented males should thus increase over the breeding season. Both predictions were supported by the experimental data. Our model shows how such patterns can emerge from the optimization of resource allocation to signaling in a competitive situation. The key determinants of the honesty and dynamics of sexual signaling are the condition dependency of male survival, the initial frequency distribution of nutritional condition in the male population, and the cost of signaling.
Full-text · Article · Oct 2009 · The American Naturalist
[Show abstract][Hide abstract] ABSTRACT: Animal social networks can be extremely complex and are characterized by highly non-random interactions between group members. However, very little is known about the underlying factors affecting interaction preferences, and hence network structure. One possibility is that behavioural differences between individuals, such as how bold or shy they are, can affect the frequency and distribution of their interactions within a network. We tested this using individually marked three-spined sticklebacks (Gasterosteus aculeatus), and found that bold individuals had fewer overall interactions than shy fish, but tended to distribute their interactions more evenly across all group members. Shy fish, on the other hand, tended to associate preferentially with a small number of other group members, leading to a highly skewed distribution of interactions. This was mediated by the reduced tendency of shy fish to move to a new location within the tank when they were interacting with another individual; bold fish showed no such tendency and were equally likely to move irrespective of whether they were interacting or not. The results show that animal social network structure can be affected by the behavioural composition of group members and have important implications for understanding the spread of information and disease in social groups.
Full-text · Article · Nov 2008 · Proceedings of the Royal Society B: Biological Sciences
[Show abstract][Hide abstract] ABSTRACT: Species of the Caenorhabditis genus have been used as model systems in genetics and molecular research for more than 30 years. Despite this, basic information about their demography, in the wild and in the lab, has remained unknown until very recently. Here, we provide for the first time a closely quantified life-cycle of the gonochoristic nematode C. remanei. Using C. elegans protocols, modified for an outcrossing nematode, we estimated the basic demography for individuals of two strains (JU724 and MY12-G) which were recently isolated from the wild. We used a half-sib breeding design to estimate the phenotypic variance of traits of related (within line) and unrelated individuals (between lines) of the two strains cultured in a common environment in the lab. Comparisons between these strains showed that JU724 was characterized by significantly lower overall lifetime fecundity and by differences in age-specific fecundity relative to MY12-G, but there were no differences in their life expectancy and reproductive lifespan. We found high phenotypic variance among all traits. The variance within lines was relatively high compared to the low variation between lines. We suggest this could be the result of high gene flow in these wild-type strains. Finally, comparisons between species suggest that, despite the differences in reproductive strategies (i.e., sex ratios, lifetime fecundity), C. remanei has developmental time similar to the hermaphroditic N2 strain of C. elegans.
Preview · Article · Oct 2008 · Journal of nematology
[Show abstract][Hide abstract] ABSTRACT: Harvest data are commonly used as proxy for count data, especially in studies of long-term temporal and spatial patterns of population fluctuations. However, usually the concurrence of the conclusions based on different types of data is impossible to verify due to the lack of count data. Here, we use annual (1964–2004) harvest and population census data for capercaillie, black grouse and hazel grouse from 14 game management districts covering Finland, and demonstrate some mismatch in the information that these data sets provide. Overall, linear regressions of annual harvest against population count give a reasonable fit, but the slopes are less than 1 in every species. Harvest bags have been proportionally larger in north and eastern Finland than in southwestern Finland, with marked species-specific differences. Considering population variation, the CV% in the census data (30–50%) is consistently smaller than it is in the harvest data (60–70%). Most importantly, conclusions on the spatio-temporal patterns of the population dynamics are different if based on harvest rather than count data. In capercaillie, synchrony decreases faster with distance according to the harvest data, while in black grouse and hazel grouse the census data show the steeper decline. In addition, the autocorrelation coefficients in the census time series are higher in capercaillie and black grouse than in harvest data, but in hazel grouse the opposite is true. Finally, the parameter estimates for a second order autoregressive model using different data sets differ, and these differences are species-specific. Despite the fact that annual harvest is a positive and linear function of annual grouse population density, the pattern of population dynamics derived from the bag data is different from that shown by the census data. This result urges caution in using wildlife bag data as reliable indices of population dynamics.deceased August 2008.
[Show abstract][Hide abstract] ABSTRACT: Most studies of female mating preferences have found preferences for males with greater trait expression. This has led to the suggestion that most female preferences are in the direction of greater sensory stimulation and may be the result of pre-existing sensory biases. Recently, studies have revealed that mating preferences can be lost or reversed, even in species where a pre-existing sensory bias appears to be the basis of female preferences. These studies concentrate on changes in female preferences on evolutionary timescales, and there is little evidence of whether female mating preferences based on pre-existing sensory biases can be altered by individual experience. Using green swordtail fish, we investigated whether female preferences for less ornamented males can be induced by manipulating early social experience. Throughout their early life females were exposed to either all long-sworded males, all short-sworded males or alternating long- and short-sworded males. Restricting experience in this way resulted in only females with experience restricted to short-sworded males developing any consistent preference, and this was for short-sworded males. This is the first evidence that female preferences based on pre-existing sensory biases can be altered ontogenetically and indicates such preferences can be remarkably labile.
[Show abstract][Hide abstract] ABSTRACT: Summary 1. The concept of site-dependent population regulation combines the ideas of Ideal Free Distribution-type of habitat settlement and density dependence in a vital rate mediated by habitat heterogeneity. The latter is also known as habitat heterogeneity hypothesis. Site-dependent population regulation hypothesis predicts that increasing population density should lead to inhabitation of increasingly poor territories and decreasing per capita population growth rate. An alternative mechanism for population regulation in a territorial breeding system is interference competition. However, this would be expected to cause a more even decrease in individual success with increasing density than site-dependent regulation. 2. We tested these ideas using long-term (1975-99) population data from a goshawk Accipiter gentilis population in Eastern Westphalia, Germany. 3. Goshawk territory occupancy patterns and reproduction parameters support predic- tions of site-dependent population regulation: territories that were occupied more often and earlier had a higher mean brood size. Fecundity did not decrease with increasing density in best territories. 4. Using time-series modelling, we also showed that the most parsimonious model explaining per capita population growth rate included annual mean habitat quality, weather during the chick rearing and autumn period and density as variables. This model explained 63% of the variation in per capita growth rate. The need for including habitat quality in the time-series model provides further support for the idea of site-dependent population regulation in goshawk.
[Show abstract][Hide abstract] ABSTRACT: Comparative evaluation mechanisms of mate choice in relation to social composition of potential mates have not been considered in nonhuman animals. Models of rational decision making suggest that when choice is based on absolute values, the addition of a third option should take choices from the original 2 options in proportion to their original shares and not result in an increase in the absolute preference for any of the 3 options in the set. However, studies of foraging behavior have shown that choice alternatives are often not irrelevant, specifically when preference is based on 2 or more dimensions (multiple cues) and when the third option is an asymmetrically dominated "decoy" (i.e., it has a lower value than both original options on one dimension but is only lower than one of the 2 original options on the other dimension). Asymmetrically dominated decoys are predicted to increase preference for the option that dominates it on both dimensions if mate choice is context dependent. We tested whether mate choice is dependent on or independent of social context in green swordtails, a species where females commonly use multiple cues in mate choice decisions. Addition of a third, decoy, male to the set of options resulted in females shifting preference away from the phenotype of male that each preferred in binary comparisons. Consequently, although mate choice was context dependent, the asymmetrically dominated decoy effect was not observed. Instead, females showed negative frequency-dependent preference for the rare-male phenotype, which may act to maintain genetic variation under sexual selection. Copyright 2008, Oxford University Press.
Full-text · Article · Jun 2008 · Behavioral Ecology
[Show abstract][Hide abstract] ABSTRACT: Carotenoids are responsible for much of the yellow, orange and red pigmentation in the animal kingdom, and the importance of such coloration as an honest signal of individual quality has received widespread attention. In particular, owing to the multiple roles of carotenoids as pigments, antioxidants and immunostimulants, carotenoid-based coloration has been suggested to advertise an individual's antioxidant or immune defence capacity. However, it has recently been argued that carotenoid-based signals may in fact be advertising the availability of different antioxidants, many of which (including various vitamins, antioxidant enzymes and minerals) are colourless and so would be uninformative as components of a visual signal, yet often have greater biological activity than carotenoids. We tested this hypothesis by feeding male sticklebacks (Gasterosteus aculeatus) a diet containing a fixed level of carotenoids and either low or high, but biologically realistic levels of the colourless antioxidant vitamins C and E. High-antioxidant diet males produced significantly more intensely coloured (but not larger) carotenoid-based regions of nuptial coloration and were preferred over size-matched males of the opposite diet treatment in mate-choice trials. Furthermore, there were positive correlations between an individual's somatic antioxidant activity and signal intensity. Our data suggest that carotenoid-based ornaments may honestly signal an individual's availability of non-carotenoid antioxidants, allowing females to make adaptive mate-choice decisions.
[Show abstract][Hide abstract] ABSTRACT: Despite convincing evidence that carotenoid availability can have positive physiological effects, we still lack information on the functional consequences of carotenoid limitation at the behavioral level. Given the role carotenoids play in mitigating oxidative stress produced during physical activity and as immunostimulants, one behavioral function on which they may have a significant impact is an individual's capacity to provide parental care. We tested this hypothesis using three-spined sticklebacks (Gasterosteus aculeatus), a species in which males provide obligate and intensive paternal care. Males were fed either high or low (but biologically realistic) levels of carotenoids and monitored throughout incubation, during which we quantified 2 key aspects of parental care: their ability to fan their eggs under normoxic and hypoxic conditions (when both the costs and requirements of fanning increase) and their ability to defend their nest against a simulated conspecific male. High-carotenoid diet males fanned their eggs at a significantly higher rate during hypoxic (but not normoxic) conditions and had higher clutch hatching success than males fed the low-carotenoid diet. There was no evidence that they defended their nest more aggressively. Furthermore, low-carotenoid diet males also appeared to engage in cannibalization of their clutch. These results demonstrate that dietary carotenoid availability can affect a male's ability to provide parental care, and we discuss the potential mechanisms and implications of this finding. Copyright 2007, Oxford University Press.
Full-text · Article · Aug 2007 · Behavioral Ecology
[Show abstract][Hide abstract] ABSTRACT: Some of the most spectacular exaggerated sexual ornaments are carotenoid dependent. It has been suggested that such ornaments have evolved because carotenoid pigments are limiting for both signal expression and in their role as antioxidants and immunostimulants. An implicit assumption of this hypothesis is that males which can afford to produce more elaborate carotenoid-dependent displays are signalling their enhanced ability to resist parasites, disease or oxidative stress and hence would be predicted to live longer. Therefore, in species with carotenoid-dependent ornaments where a parent's future longevity is crucial for determining offspring survival, there should be a mating preference for partners that present the lowest risk of mortality during the breeding attempt, as signalled by the ability to allocate carotenoids to sexual displays. In an experimental study using three-spined sticklebacks (Gasterosteus aculeatus), we show that when dietary carotenoid intake is limited, males attempt to maintain their sexual ornament at the expense of body carotenoids and hence suffer from reduced reproductive investment and a shorter lifespan. These males also suffer from an increased susceptibility to oxidative stress, suggesting that this may constitute the mechanism underlying the increased rate of ageing. Furthermore, in pairwise mate-choice trials, females preferred males that had a greater access to carotenoids and chance of surviving the breeding season, suggesting that females can make adaptive mate choice decisions based on a male's carotenoid status and potential future longevity.
Full-text · Article · Aug 2007 · Proceedings of the Royal Society B: Biological Sciences