Research progress in avian dispersal behavior

Dispersal, defined as a linear spreading movement of individuals away from others of the population is a fundamental characteristic of organisms in nature. Dispersal is a central concept in ecological, behavioral and evolutionary studies, driven by different forces such as avoidance of inbreeding depression, density-dependent competition and the need to change breeding locations. By effective dispersal, organisms can enlarge their geographic range and adjust the dynamic, sex ratio and genetic compositions of a population. Birds are one of the groups that are studied intensively by human beings. Due to their diurnal habits, diverse life history strategies and complex movement, birds are also ideal models for the study of dispersal behaviors. Certain topics of avian dispersal including sex-biased, asymmetric dispersal caused by differences in body conditions, dispersal processes, habitat selection and long distance dispersal are discussed here. Bird-ringing or marking, radio-telemetry and genetic markers are useful tools widely applied in dispersal studies. There are three major challenges regarding theoretical study and methodology research of dispersal: (1) improvement in research methodology is needed, (2) more in-depth theoretical research is necessary, and (3) application of theoretical research into the conservation efforts for threatened birds and the management of their habitats should be carried out immediately. __________ Translated from Acta Ecologica Sinica, 2008, 28(4): 1354–1365 [译自: 生态学报]     

Research progress in avian dispersal behavior

Dispersal, defined as a linear spreading move-ment of individuals away from others of the population is a fundamental characteristic of organisms in nature. Dispersal is a central concept in ecological, behavioral and evolutionary studies, driven by different forces such as avoidance of inbreeding depression, density-dependent competition and the need to change breeding locations. By effective dispersal, organisms can enlarge their geo-graphic range and adjust the dynamic, sex ratio and gen-etic compositions of a population. Birds are one of the groups that are studied intensively by human beings. Due to their diurnal habits, diverse life history strategies and complex movement, birds are also ideal models for the study of dispersal behaviors. Certain topics of avian dispersal including sex-biased, asymmetric dispersal caused by differences in body conditions, dispersal pro-cesses, habitat selection and long distance dispersal are discussed here. Bird-ringing or marking, radio-telemetry and genetic markers are useful tools widely applied in dispersal studies. There are three major challenges regard-ing theoretical study and methodology research of dis-persal: (1) improvement in research methodology is needed, (2) more in-depth theoretical research is neces-sary, and (3) application of theoretical research into the conservation efforts for threatened birds and the manage-ment of their habitats should be carried out immediately.     

A comparison of individual‐based genetic distance metrics for landscape genetics

A major aim of landscape genetics is to understand how landscapes resist gene flow and thereby influence population genetic structure. An empirical understanding of this process provides a wealth of information that can be used to guide conservation and management of species in fragmented landscapes and also to predict how landscape change may affect population viability. Statistical approaches to infer the true model among competing alternatives are based on the strength of the relationship between pairwise genetic distances and landscape distances among sampled individuals in a population. A variety of methods have been devised to quantify individual genetic distances, but no study has yet compared their relative performance when used for model selection in landscape genetics. In this study, we used population genetic simulations to assess the accuracy of 16 individual‐based genetic distance metrics under varying sample sizes and degree of population genetic structure. We found most metrics performed well when sample size and genetic structure was high. However, it was much more challenging to infer the true model when sample size and genetic structure was low. Under these conditions, we found genetic distance metrics based on principal components analysis were the most accurate (although several other metrics performed similarly), but only when they were derived from multiple principal components axes (the optimal number varied depending on the degree of population genetic structure). Our results provide guidance for which genetic distance metrics maximize model selection accuracy and thereby better inform conservation and management decisions based upon landscape genetic analysis.     

Consequences of population topology for studying gene flow using link‐based landscape genetic methods

Many landscape genetic studies aim to determine the effect of landscape on gene flow between populations. These studies frequently employ link‐based methods that relate pairwise measures of historical gene flow to measures of the landscape and the geographical distance between populations. However, apart from landscape and distance, there is a third important factor that can influence historical gene flow, that is, population topology (i.e., the arrangement of populations throughout a landscape). As the population topology is determined in part by the landscape configuration, I argue that it should play a more prominent role in landscape genetics. Making use of existing literature and theoretical examples, I discuss how population topology can influence results in landscape genetic studies and how it can be taken into account to improve the accuracy of these results. In support of my arguments, I have performed a literature review of landscape genetic studies published during the first half of 2015 as well as several computer simulations of gene flow between populations. First, I argue why one should carefully consider which population pairs should be included in link‐based analyses. Second, I discuss several ways in which the population topology can be incorporated in response and explanatory variables. Third, I outline why it is important to sample populations in such a way that a good representation of the population topology is obtained. Fourth, I discuss how statistical testing for link‐based approaches could be influenced by the population topology. I conclude the article with six recommendations geared toward better incorporating population topology in link‐based landscape genetic studies.     

PCR‐based isolation of multigene families: lessons from the avian MHC class IIB

The amount of sequence data available today highly facilitates the access to genes from many gene families. Primers amplifying the desired genes over a range of species are readily obtained by aligning conserved gene regions, and laborious gene isolation procedures can often be replaced by quicker PCR‐based approaches. However, in the case of multigene families, PCR‐based approaches bear the often ignored risk of incomplete isolation of family members. This problem is most prominent in gene families with highly variable and thus unpredictable number of gene copies among species, such as in the major histocompatibility complex (MHC). In this study, we (i) report new primers for the isolation of the MHC class IIB (MHCIIB) gene family in birds and (ii) share our experience with isolating MHCIIB genes from an unprecedented number of avian species from all over the avian phylogeny. We report important and usually underappreciated problems encountered during PCR‐based multigene family isolation and provide a collection of measures to help significantly improving the chance of successfully isolating complete multigene families using PCR‐based approaches.     

Pollen transport differs among bees and flies in a human‐modified landscape

Aim Dispersal distances of insect pollinators are critical in defining their contribution to landscape‐wide pollen movement and ultimately gene flow in natural and agricultural systems. We ask whether bee and fly pollinator taxa differ in their dispersal distances and transport of viable pollen in a human‐modified system. Location Canterbury and Otago region, South Island, New Zealand. Methods We captured pollen‐carrying insects travelling outside of a model mass‐flowering agricultural crop, Brassica rapa, using insect flight intercept traps at five distances (0, 100, 200, 300 and 400 m) from the pollen source. We examined pollen loads and pollen viability to determine whether pollen transport distance and viability differ among pollinator taxa. Results A total of 5453 insects were collected of which 717 individuals from 26 insect taxa were positively identified as dispersing pollen up to 400 m from the source. These taxa consisted of four species from two bee families (Hymenoptera: Apidae and Halictidae), and eight species from four fly families (Diptera: Bibiondae, Stratiomyidae, Syrphidae and Tachinidae). Apidae generally carried higher pollen loads and more viable pollen than most fly taxa. Taxa in the fly families Stratiomyidae and Syrphidae, however, carried pollen to 400 m, which is further than both bee families. Main conclusions A diverse array of wild and managed flower visitors can transport viable pollen from a pollen source to at least 400 m. Knowledge of the differences in transport distances among generalist pollinators in human‐modified environments is crucial to understand the potential extent to which (1) pollen transport can facilitate gene flow and (2) unwanted hybridization may occur between crops and related weeds.     

Fine‐scale genetics of subterranean syncarids

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