Release of phylogenetic constraints through low resource heterogeneity: the case of gall-inducing sawflies

Abstract. 1. A group of six unusual sawfly species, which do not conform to the phylogenetic constraints hypothesis as it has been applied to sawflies, was examined in natural populations. All species were in the genus Pontania (Hymenoptera: Tenthredinidae), which induce galls on leaves of willow species (Salicaceae). An understanding of these non‐conformist species was important as a test of the validity of the general hypothesis. 2. The six species of sawfly, Pontania mandshurica, P. cf. arcticornis, P. aestiva, P. arcticornis, P. pacifica, and P. nr. pacifica, showed no oviposition preference for long, vigorous shoots, in contrast to 37 documented tenthredinid species that have demonstrated such a preference. Rather, the non‐conformist species attacked the shortest shoot length classes more frequently and larval establishment in galls was successful. 3. The evident escape from the phylogenetic constraint, which commonly limits sawfly attack to the most vigorous shoots in a willow population, resulted from low apparent heterogeneity of the resources exploited by these Pontania species. At the time of female oviposition, shoots and leaves were too uniform to allow discrimination by females among shoot length classes, resulting in random, or near random attack of shoots. 4. The unusual relative uniformity of resources to which sawflies were exposed resulted from several characteristics. (1) Females emerged early relative to shoot growth phenology, making discrimination among shoot length and vigour difficult or impossible. (2) Low heterogeneity in leaf length resulted in resource similarity independent of shoot length. (3) Abscission of leaves occurred after emergence of larvae from leaf galls so that differential abscission of leaves in relation to shoot length became irrelevant. (4) In some cases, low variance in shoot lengths was evident in old ramets lacking long, vigorous shoots. Probably as a result of low resource heterogeneity, larvae survived well across all shoot length classes, revealing no ovipositional preference and larval performance linkage related to the exploitation of the longest shoot length classes in a population of willows, as in the conformist species. Therefore, larval survival did not provide positive feedback on female preferential behaviour for long shoots, as in the conformist species studied.     

Do mothers prefer helpers or smaller litters? Birth sex ratio and litter size adjustment in cotton-top tamarins (Saguinus oedipus)

Sex allocation theory has been a remarkably productive field in behavioral ecology with empirical evidence regularly supporting quantitative theoretical predictions. Across mammals in general and primates in particular, however, support for the various hypotheses has been more equivocal. Population‐level sex ratio biases have often been interpreted as supportive, but evidence for small‐scale facultative adjustment has rarely been found. The helper repayment (HR) also named the local resource enhancement (LRE) hypothesis predicts that, in cooperatively breeding species, mothers invest more in the sex which assists with rearing future offspring and that this bias will be more pronounced in mothers who require extra assistance (i.e., due to inexperience or a lack of available alloparents). We tested these hypotheses in captive cotton‐top tamarins (Saguinus oedipus) utilizing the international studbook and birth records obtained through a questionnaire from ISIS‐registered institutions. Infant sex, litter size, mother's age, parity, and group composition (presence of nonreproductive subordinate males and females) were determined from these records. The HR hypothesis was supported over the entire population, which was significantly biased toward males (the “helpful” sex). We found little support for helper repayment at the individual level, as primiparous females and those in groups without alloparents did not exhibit more extreme tendencies to produce male infants. Primiparous females were, however, more likely to produce singleton litters. Singleton births were more likely to be male, which suggests that there may be an interaction between litter size adjustment and sex allocation. This may be interpreted as supportive of the HR hypothesis, but alternative explanations at both the proximate and ultimate levels are possible. These possibilities warrant further consideration when attempting to understand the ambiguous results of primate sex ratio studies so far.     

Kinship and similarity in residency status structure female social networks in black‐and‐white colobus monkeys (colobus vellerosus)

Kinship shapes female social networks in many primate populations in which females remain in their natal group to breed. In contrast, it is unclear to which extent kinship affects the social networks in populations with female dispersal. Female Colobus vellerosus show routine facultative dispersal (i.e., some females remain philopatric and others disperse). This dispersal pattern allowed us to evaluate if facultative dispersed females form social networks shaped by an attraction to kin, to social partners with a high resource holding potential, or to similar social partners in terms of maturational stage, dominance rank, and residency status. During 2008 and 2009, we collected behavioral data via focal and ad libitum sampling of 61 females residing in eight groups at Boabeng‐Fiema, Ghana. We determined kinship based on partial pedigrees and genotypes at 17 short tandem repeat loci. Kinship influenced coalition and affiliation networks in three groups consisting of long‐term resident females with access to a relatively high number of female kin. In contrast, similar residency status was more important than kinship in structuring the affiliation network in one of two groups that contained recent female immigrants. In populations with female dispersal, the occurrence of kin structured social networks may not only depend on the kin composition of groups but also on how long the female kin have resided together. We found no consistent support for females biasing affiliation toward partners with high resource holding potential, possibly due to low levels of contest competition and small inter‐individual differences in resource holding potential. Am J Phys Anthropol 153:365–376, 2014. © 2013 Wiley Periodicals, Inc.     

Microbes are not bound by sociobiology: Response to Kümmerli and Ross‐Gillespie (2013)

In recent years, sociobiology has been extended to microorganisms. Viewed through this lens, the microbial world is replete with cooperative behaviors. However, little attention has been paid to alternate hypotheses, making many studies self‐confirming. Somewhat apart is a recent analysis of pyoverdin production—a paradigmatic public good and social trait—by Pseudomonas, which has revealed discord between predictions arising from sociobiology and the biology of microbes. This led the authors, Zhang and Rainey (Z&R), to question the generality of the conclusion that pyoverdin is a social trait, and to question the fit between the sociobiology framework and microbiology. This has unsettled Kümmerli and Ross‐Gillespie (K&R), who in a recent “Technical Comment” assert that arguments presented by Z&R are flawed, their experiments technically mistaken, and their understanding of social evolution theory naive. We demonstrate these claims to be without substance and show the conclusions of K&R to be based on a lack of understanding of redox chemistry and on misinterpretation of data. We also point to evidence of cherry‐picking and raise the possibility of confirmation bias. Finally, we emphasize that the sociobiology framework applied to microbes is a hypothesis that requires rigorous and careful appraisal.     

LESS IS MORE: SELECTIVE ADVANTAGES CAN EXPLAIN THE PREVALENT LOSS OF BIOSYNTHETIC GENES IN BACTERIA

Bacteria that have adapted to nutrient‐rich, stable environments are typically characterized by reduced genomes. The loss of biosynthetic genes frequently renders these lineages auxotroph, hinging their survival on an environmental uptake of certain metabolites. The evolutionary forces that drive this genome degradation, however, remain elusive. Our analysis of 949 metabolic networks revealed auxotrophies are likely highly prevalent in both symbiotic and free‐living bacteria. To unravel whether selective advantages can account for the rampant loss of anabolic genes, we systematically determined the fitness consequences that result from deleting conditionally essential biosynthetic genes from the genomes of Escherichia coli and Acinetobacter baylyi in the presence of the focal nutrient. Pairwise competition experiments with each of 20 mutants auxotrophic for different amino acids, vitamins, and nucleobases against the prototrophic wild type unveiled a pronounced, concentration‐dependent growth advantage of around 13% for virtually all mutants tested. Individually deleting different genes from the same biosynthesis pathway entailed gene‐specific fitness consequences and loss of the same biosynthetic genes from the genomes of E. coli and A. baylyi differentially affected the fitness of the resulting auxotrophic mutants. Taken together, our findings suggest adaptive benefits could drive the loss of conditionally essential biosynthetic genes.     

西藏小昌都黑白仰鼻猴的雄婴照料:能量胁迫导致?

雄猴照料婴猴行为通常都是从雄猴的角度来分析该行为具有何种适应功能,很少有研究关心为什么雌猴会让雄猴参与照料活动。该文通过西藏小昌都黑白仰鼻猴群的系统观察取样,采用回归分析雄婴照料行为季节变动与婴猴年龄及生态因子（环境温度、食物供应）之间的关系,试图分析是否由于能量胁迫导致雌猴让雄猴参与照料活动,并通过分析高能量胁迫季节（环境温度低、食物缺乏,婴猴年幼需要雌猴携带多）与低能量胁迫季节（环境温度高、食物丰富,婴猴年长需要雌猴携带少）雄婴照料行为差异检验了能量胁迫假说。结果表明雄婴照料行为与温度呈负相关函数,而雌猴照料婴猴行为与温度呈正相关函数;在高能量胁迫的季节,雄猴参与照料行为多,而在低能量胁迫的季节雄猴照料行为少。因此,作者认为是能量胁迫迫使雌猴放弃部分照料婴猴的机会,雄猴利用照料机会获得了其他利益。     

Computational modeling of epithelial–mesenchymal transformations

An epithelial–mesenchymal transformation (EMT) involves alterations in cell–cell and cell–matrix adhesion, the detachment of epithelial cells from their neighbors, the degradation of the basal lamina and acquisition of mesenchymal phenotype. Here we present Monte Carlo simulations for a specific EMT in early heart development: the formation of cardiac cushions. Cell rearrangements are described in accordance with Steinberg's differential adhesion hypothesis, which states that cells possess a type-dependent adhesion apparatus and are sufficiently motile to give rise to the tissue conformation with the largest number of strong bonds. We also implement epithelial and mesenchymal cell proliferation, cell type change and extracellular matrix production by mesenchymal cells. Our results show that an EMT is promoted more efficiently by an increase in cell–substrate adhesion than by a decrease in cell–cell adhesion. In addition to cushion tissue formation, the model also accounts for the phenomena of matrix invasion and mesenchymal condensation. We conclude that in order to maintain epithelial integrity during EMT the number of epithelial cells must increase at a controlled rate. Our model predictions are in qualitative agreement with available experimental data.