Adapting to an invasive species: toxic cane toads induce morphological change in Australian snakes.
(33/2357)
The arrival of invasive species can devastate natural ecosystems, but the long-term effects of invasion are less clear. If native organisms can adapt to the presence of the invader, the severity of impact will decline with time. In Australia, invasive cane toads (Bufo marinus) are highly toxic to most snakes that attempt to eat them. Because snakes are gape-limited predators with strong negative allometry for head size, maximum relative prey mass (and thus, the probability of eating a toad large enough to be fatal) decreases with an increase in snake body size. Thus, the arrival of toads should exert selection on snake morphology, favoring an increase in mean body size and a decrease in relative head size. We tested these predictions with data from specimens of four species of Australian snakes, collected over >80 years. Geographic information system layers provided data on the duration of toad exposure for each snake population, as well as environmental variables (latitude, precipitation, and temperature). As predicted, two toad-vulnerable species (Pseudechis porphyriacus and Dendrelaphis punctulatus) showed a steady reduction in gape size and a steady increase in body length with time since exposure to toads. In contrast, two species at low risk from toads (Hemiaspis signata and Tropidonophis mairii) showed no consistent change in these morphological traits as a function of the duration of toad exposure. These results provide strong evidence of adaptive changes in native predators as a result of the invasion of toxic prey. (+info)
Adherence to the traditional mediterranean diet is inversely associated with body mass index and obesity in a spanish population.
(34/2357)
The Mediterranean diet is a healthy eating pattern with protective effects on chronic diseases. The purpose of this study was to assess the relation between BMI and obesity and the level of adherence to the traditional Mediterranean diet. The subjects were Spanish men (n = 1547) and women (n = 1615) aged 25-74 y who were examined in 1999-2000, in a population-based, cross-sectional survey in the northeast of Spain (Girona). Dietary intake was assessed using a FFQ. A Mediterranean diet score, including foods considered to be characteristic components of the traditional Mediterranean diet (vegetables, fruits, pulses, nuts, fish, meat, cereals, olive oil, and wine) was created. An increase of 5 U in the dietary score was associated with a change in the BMI of 0.43 (P = 0.030) and 0.68 (P = 0.007), after controlling for potential confounders, in men and women, respectively. The obesity risk decreased in men (P = 0.010) and women (P = 0.013) with increasing adherence to the traditional Mediterranean dietary pattern. The population in the top tertile of this score were less likely to be obese in both genders [odds ratio (OR) and (95% CI): 0.61 (0.40-0.92) in men; 0.61 (0.40-0.93) in women] after adjusting for potential confounders. These data suggest that the traditional Mediterranean dietary pattern is inversely associated with BMI and obesity. This finding may be useful in the development of dietary approaches for dietary counseling and the prevention of obesity. (+info)
Breast cancer and the brain: a neurodevelopmental hypothesis to explain the opposing effects of caloric deprivation during the Dutch famine of 1944-1945 on breast cancer and its risk factors.
(35/2357)
Most studies on calorie deprivation and cancer risk in rodents show reductions in tumor occurrence. However, the few human studies on calorie restriction are conflicting. An overview is given of results in the DOM (diagnostic onderzoek mammacarcinoom) cohorts among women exposed to the Dutch Famine of 1944-1945. Opposing effects were found on risk factors (shortening of leg length, later menarche, and earlier menopause), whereas urinary estrogens and plasma insulin-like growth factor (IGF)-1 and IGF binding protein-3 were increased, as was breast cancer itself. Exposure between 2 and 10 y old was an unexpected window of susceptibility to the effects of calorie deprivation. The effects of famine exposure were most clearly seen in women who never gave birth. These opposing observations can be explained by a neurodevelopmental hypothesis on set-point shifts at the level of the diencephalons/hypothalamus, either directly or from rebound effects. Such a mechanism reflects old evolutionary adaptation systems in lower and higher organisms to cope with periods of stress and famine by adjusting, for example, reproductive functions. These effects in exposed women may later also affect their unexposed offspring. This hypothesis provides several testable, hormone-mediated corollaries on the relationships between the role of calories in a Westernized lifestyle and human cancer risk. The underlying developmental perspective, as opposed to a risk factor approach, can explain why certain ages, even before breast development, are especially sensitive to effects of large fluctuations in calories. The observations presented may have implications for preventive strategies such as promoting moderation of calorie intake to curb cancer risks. (+info)
Differences in sensory projections between macro- and microchaetes in Drosophilid flies.
(36/2357)
From examination of the central axonal projections of sensory bristles on the notum of several species of Drosophilidae, we demonstrate different features that may indicate different functions for macro- and microchaetes. The large macrochaetes have conserved arborizations that correlate with their conserved position. Nevertheless, we find evidence for only two discrete projection patterns for bristles in the dorsocentral (DC) row, even when there may be four or five bristles present. We show that the small microchaetes of Drosophila melanogaster display regional specificity and subsets of contiguous bristles project to a common region in the thoracic ganglion. Interestingly, the axons of each of these subsets also form a specific fasciculation group on the scutum before joining the axon of a particular macrochaete. The positions of microchaetes on the scutum and the shape of the fasciculation groups vary between closely related species. There is no correlation between body size, bristle patterns, and fasciculation patterns. Furthermore, none of these traits correlate with the phylogenetic relationships between the species studied. We discuss the possibility that macro- and microchaetes may have different functions and that these have implications for evolutionary constraints on bristle patterns. (+info)
Female preference for multiple condition-dependent components of a sexually selected signal.
(37/2357)
Theoretical models explain the evolution of multi-cue mate-choice decisions from a trade-off between benefits owing to improved assessment of potential mates and costs linked to the use of multiple signals. However, empirical support for these basic assumptions is lacking. In field crickets (Gryllus campestris) we experimentally investigated the female preference to variation in two key components of the male calling song: carrier frequency and chirp rate. Previous studies have revealed carrier frequency and chirp rate as reliable indicators of male quality that reflect past condition and current condition, respectively. In a two-way choice experiment, females significantly preferred test songs of lower carrier frequency and higher chirp rate, but prioritized the carrier frequency over the chirp rate. Hence, the static long-term indicator of mate quality was weighted more than the dynamic short-term one. Our results thus indicate that females integrate information from independent condition-dependent cues to discriminate between available males in mate-choice decisions. (+info)
The effect of energy reserves on social foraging: hungry sparrows scrounge more.
(38/2357)
Animals often use alternative strategies when they compete for resources, but it is unclear in most cases what factors determine the actual tactic followed by individuals. Although recent models suggest that the internal state of animals may be particularly important in tactic choice, the effects of state variables on the use of alternative behavioural forms have rarely been demonstrated. In this study, using experimental wind exposure to increase overnight energy expenditure, we show that flock-feeding house sparrows (Passer domesticus) with lowered energy reserves increase their use of scrounging (exploiting others' food findings) during their first feed of the day. This result is in accordance with the prediction of a state-dependent model of use of social foraging tactics. We also show that scrounging provides less variable feeding rates and patch finding times than the alternative tactic. These latter results support the theoretical assumption that scrounging is a risk-averse tactic, i.e. it reduces the risk of immediate starvation. As the level of energy reserves predicts the use of social foraging tactics, we propose that selection should favour individuals that monitor the internal state of flock mates and use this information to adjust their own tactic choice. (+info)
Predicting shifts in dynamics of cannibalistic field populations using individual-based models.
(39/2357)
The occurrence of qualitative shifts in population dynamical regimes has long been the focus of population biologists. Nonlinear ecological models predict that these shifts in dynamical regimes may occur as a result of parameter shifts, but unambiguous empirical evidence is largely restricted to laboratory populations. We used an individual-based modelling approach to predict dynamical shifts in field fish populations where the capacity to cannibalize differed between species. Model-generated individual growth trajectories that reflect different population dynamics were confronted with empirically observed growth trajectories, showing that our ordering and quantitative estimates of the different cannibalistic species in terms of life-history characteristics led to correct qualitative predictions of their dynamics. (+info)
Genetic basis of variation in morphological and life-history traits of a wild population of pink salmon.
(40/2357)
Understanding the genetic basis of phenotypic variation is essential for predicting the direction and rate of phenotypic evolution. We estimated heritabilities and genetic correlations of morphological (fork length, pectoral and pelvic fin ray counts, and gill arch raker counts) and life-history (egg number and individual egg weight) traits of pink salmon (Oncorhynchus gorbuscha) from Likes Creek, Alaska, in order to characterize the genetic basis of phenotypic variation in this species. Families were created from wild-caught adults, raised to the fry stage in the lab, released into the wild, and caught as returning adults and assigned to families using microsatellite loci and a growth hormone locus. Morphological traits were all moderately to highly heritable, but egg number and egg weight were not heritable, suggesting that past selection has eliminated additive genetic variation in egg number and egg weight or that there is high environmental variance in these traits. Genetic correlations were similar for nonadjacent morphological traits and adjacent traits. Genetic correlations predicted phenotypic correlations fairly accurately, but some pairs of traits with low genetic correlations had high phenotypic correlations, and vice versa, emphasizing the need to use caution when using phenotypic correlations as indices of genetic correlations. This is one of only a handful of studies to estimate heritabilities and genetic correlations for a wild population. (+info)