Fruit size and shape: Allometry at different taxonomic levels in bird-dispersed plants

Summary The likelihood that a plant's seeds will be dispersed by fruit-eating birds may depend upon the size and shape of its fruits. Assuming that elongate fruits can be swallowed more easily than spherical fruits of equal volume and that plant fitness is enhanced by seed dispersal by many individuals and species of birds, natural selection should favour increasing fruit elongation with increasing fruit size in bird-dispersed plants. According to this view, this allometric pattern would be adaptive. Alternatively, fruit shape in bird-dispersed plants may be constrained by development or phylogeny. To determine whether there was any evidence to support the adaptive allometry hypothesis, we examined allometric relationships between length and diameter in fruits and seeds in a group of neotropical bird-dispersed plant species. Using the major axis technique, we regressed ln(diameter) on ln(length) for fruits and seeds at various taxonomic levels: (1) within individual trees ofOcotea tenera (Lauraceae) (2) among 19 trees within a population ofO. tenera, as well as among pooled fruits from multiple trees within 20 other species in the Lauraceae, (3) among 25 sympatric species within a plant family (Lauraceae) and (4) among 167 species representing 63 angiosperm families within a plant community in Monteverde, Costa Rica. At most taxonomic levels, a tendency for fruit length to increase more rapidly than fruit diameter among fruits (negative allometry) occurred more frequently than expected by chance. Estimated slopes of the regressions of fruit length on fruit diameter were < 1 within 15 of the 19 individualO. tenera trees, among tree means withinO. tenera, among pooled fruits within 16 of the 20 other species in the Lauraceae, among species means within the Lauraceae and among means of all bird-dispersed species in the lower montane forests of Monteverde. Seed allometry showed similar patterns, although for both fruits and seeds the broad confidence intervals of the slopes estimated by major axis regression overlapped 1 in many cases. Among the 63 Monteverde family means, fruit length and diameter scaled isometrically. Based on measurements of ontogenetic changes in fruit shape in a single species,O. viridifolia, we found no evidence that negative allometry in fruit shape within the Lauraceae was an inevitable consequence of developmental constraints. Instead, increasing elongation of fruits and seeds in certain plant taxa is consistent with adaptation to gape-limited avian seed dispersers. Contrary results from vertebrate-dispersed species from Malawi and Spain may reflect differences between the New and Old World in plant taxa, seed dispersers or evolutionary history.     

Early life events carry over to influence pre-migratory condition in a free-living songbird

Conditions experienced during development can have long-term consequences for individual success. In migratory songbirds, the proximate mechanisms linking early life events and survival are not well understood because tracking individuals across stages of the annual cycle can be extremely challenging. In this paper, we first use a 13 year dataset to demonstrate a positive relationship between 1(st) year survival and nestling mass in migratory Savannah sparrows (Passerculus sandwichensis). We also use a brood manipulation experiment to show that nestlings from smaller broods have higher mass in the nest relative to individuals from larger broods. Having established these relationships, we then use three years of field data involving multiple captures of individuals throughout the pre-migratory period and a multi-level path model to examine the hypothesis that conditions during development limit survival during migration by affecting an individual's ability to accumulate sufficient lean tissue and fat mass prior to migration. We found a positive relationship between fat mass during the pre-migratory period (Sept-Oct) and nestling mass and a negative indirect relationship between pre-migratory fat mass and fledging date. Our results provide the first evidence that conditions during development limit survival during migration through their effect on fat stores. These results are particularly important given recent evidence showing that body condition of songbirds at fledging is affected by climate change and anthropogenic changes to landscape structure.     

Little effect of extrapair paternity on the opportunity for sexual selection in Savannah sparrows (Passerculus sandwichensis)

Extrapair paternity (EPP) can dramatically increase the opportunity for sexual selection if relatively few males are able to monopolize the majority of fertilizations in a population. Although recent work with birds suggests that EPP can increase the standardized variance in male reproductive success (Is) as much as 13-fold, only a male's within-pair success is typically quantified with any accuracy. In most cases, nearly half of all extrapair young are of unknown parentage. A strong, negative correlation across studies between the proportion of extrapair young for which parentage is known and the apparent effect of EPP on Is (r(s) = -0.71, P = 0.013, N = 13 studies) suggests that the incomplete sampling of extrapair sires has greatly exaggerated the influence of EPP. To achieve a more thorough accounting of EPP and its importance to variation in male fitness, we used a suite of four to six microsatellite loci to identify extrapair young and their sires in a polygynous population of Savannah sparrows (Passerculus sandwichensis). Pooling over the 2002 and 2003 breeding seasons, 79 of 116 females (68.1%) produced young outside of the pairbond and 194 of 411 offspring (47.2%) were extrapair. We identified sires for 96.4% of all young (N = 396), including sires for 92.3% of the extrapair young (N = 179), allowing us to partition Is into within-pair and extrapair components. In both years, EPP-related fitness components generated more variation in male reproductive success than the number or quality of within-pair mates. Differences among males in the number of extrapair mates alone accounted for 56.6% of Is in 2002 and for 23.6% of Is in 2003. Nonetheless, in absolute terms, the occurrence of EPP on Kent Island increased the opportunity for sexual selection less than two-fold. Averaging over the two years, Is was only 78% higher than Is,app, the variance in male reproductive success that would have occurred had EPP been nonexistent and males sired all young on their territories. Likewise, across nine socially monogamous species, we found no correlation between the extent of EPP and its effect on the opportunity for sexual selection (Is/Is,app) and only a marginally significant positive correlation between EPP and Is itself. Taken together, our results suggest that the relationship between EPP and sexual selection in birds may be much less strong and much less straightforward than commonly thought.     

Complexity in relationships between antioxidants and individual life‐history parameters in a seabird and a songbird

Selection on physiological traits is thought to mediate the evolution of individual life‐history parameters like reproduction, longevity, and the tradeoffs between them, but almost nothing is known about the relationships between physiological and life‐history parameters in the wild. Antioxidants are strong candidates to correlate with life histories because they play a critical role in preventing free radical damage to macromolecules, and many types are involved in sexual signaling and embryo provisioning. Here for the first time we present data on associations between serum antioxidant measures (antioxidant capacity and concentrations of uric acid, vitamin E and carotenoids) and indices of reproductive rate and age in two bird species. After controlling for age, 36% of the variation in hatching rate in Leach's storm‐petrels Oceanodroma leucorhoa was accounted for by a negative association with antioxidant capacity. Age was negatively associated with uric acid levels. Savannah sparrows Passerculus sandwichensis showed no association between antioxidant capacity and fledging rate, but serum β‐carotene levels were weakly positively associated with fledging rate. Because antioxidant levels are known to vary markedly within individuals over time, detection of associations between long‐term measures of reproduction and instantaneous antioxidant levels suggests strong (though not necessarily causal) relationships. Relationships between antioxidants and life histories appeared to differ in sparrows and storm‐petrels though, likely due to variation in diet, ecology, and life‐history evolution in these distantly related species.     

A Genome Wide Association Study of Mathematical Ability Reveals an Association at Chromosome 3q29, a Locus Associated with Autism and Learning Difficulties: A Preliminary Study

Mathematical ability is heritable, but few studies have directly investigated its molecular genetic basis. Here we aimed to identify specific genetic contributions to variation in mathematical ability. We carried out a genome wide association scan using pooled DNA in two groups of U.K. samples, based on end of secondary/high school national academic exam achievement: high (n = 419) versus low (n = 183) mathematical ability while controlling for their verbal ability. Significant differences in allele frequencies between these groups were searched for in 906,600 SNPs using the Affymetrix GeneChip Human Mapping version 6.0 array. After meeting a threshold of p<1.5×10⁻⁵, 12 SNPs from the pooled association analysis were individually genotyped in 542 of the participants and analyzed to validate the initial associations (lowest p-value 1.14 ×10⁻⁶). In this analysis, one of the SNPs (rs789859) showed significant association after Bonferroni correction, and four (rs10873824, rs4144887, rs12130910 rs2809115) were nominally significant (lowest p-value 3.278 × 10⁻⁴). Three of the SNPs of interest are located within, or near to, known genes (FAM43A, SFT2D1, C14orf64). The SNP that showed the strongest association, rs789859, is located in a region on chromosome 3q29 that has been previously linked to learning difficulties and autism. rs789859 lies 1.3 kbp downstream of LSG1, and 700 bp upstream of FAM43A, mapping within the potential promoter/regulatory region of the latter. To our knowledge, this is only the second study to investigate the association of genetic variants with mathematical ability, and it highlights a number of interesting markers for future study.     

Mathematical Talent is Linked to Autism

A total of 378 mathematics undergraduates (selected for being strong at “systemizing”) and 414 students in other (control) disciplines at Cambridge University were surveyed with two questions: (1) Do you have a diagnosed autism spectrum condition? (2) How many relatives in your immediate family have a diagnosed autism spectrum condition? Results showed seven cases of autism in the math group (or 1.85%) vs one case of autism in the control group (or 0.24%), a ninefold difference that is significant. Controlling for sex and general population sampling, this represents a three- to sevenfold increase for autism spectrum conditions among the mathematicians. There were 7 of 1,405 (or 0.5%) cases of autism in the immediate families of the math group vs 2 of 1,669 (or 0.1%) cases in the immediate families of the control group, which again is a significant difference. These results confirm a link between autism and systemizing, and they suggest this link is genetic given the association between autism and first-degree relatives of mathematicians.     

Cognition in Males and Females with Autism: Similarities and Differences

The male bias in autism spectrum conditions (ASC) has led to females with ASC being under-researched. This lack of attention to females could hide variability due to sex that may explain some of the heterogeneity within ASC. In this study we investigate four key cognitive domains (mentalizing and emotion perception, executive function, perceptual attention to detail, and motor function) in ASC, to test for similarities and differences between males and females with and without ASC (n = 128 adults; n = 32 per group). In the mentalizing and facial emotion perception domain, males and females with ASC showed similar deficits compared to neurotypical controls. However, in attention to detail and dexterity involving executive function, although males with ASC showed poorer performance relative to neurotypical males, females with ASC performed comparably to neurotypical females. We conclude that performance in the social-cognitive domain is equally impaired in male and female adults with ASC. However, in specific non-social cognitive domains, performance within ASC depends on sex. This suggests that in specific domains, cognitive profiles in ASC are modulated by sex.