Academic journal article Genetics

Fine-Scale Genetic Structure and Gene Dispersal in Centaurea Corymbosa (Asteraceae). II. Correlated Paternity within and among Sibships

Academic journal article Genetics

Fine-Scale Genetic Structure and Gene Dispersal in Centaurea Corymbosa (Asteraceae). II. Correlated Paternity within and among Sibships

Article excerpt

ABSTRACT

The fine-scale pattern of correlated paternity was characterized within a population of the narrow-endemic model plant species, Centaurea corymbosa, using microsatellites and natural progeny arrays. We used classical approaches to assess correlated mating within sibships and developed a new method based on pairwise kinship coefficients to assess correlated paternity within and among sibships in a spatio-temporal perspective. We also performed numerical simulations to assess the relative significance of different mechanisms promoting correlated paternity and to compare the statistical properties of different estimators of correlated paternity. Our new approach proved very informative to assess which factors contributed most to correlated paternity and presented good statistical properties. Within progeny arrays, we found that about one-fifth of offspring pairs were full-sibs. This level of correlated mating did not result from correlated pollen dispersal events (i.e., pollen codispersion) but rather from limited mate availability, the latter being due to limited pollen dispersal distances, the heterogeneity of pollen production among plants, phenological heterogeneity and, according to simulations, the self-incompatibility system.We point out the close connection between correlated paternity and the "TwoGener" approach recently developed to infer pollen dispersal and discuss the conditions to be met when applying the latter.

CORRELATED paternity refers to the fact that different offspring may be sired by the same father. Within maternal progeny arrays it is often referred to as "correlated mating" and can be expressed by the fraction of full-sib pairs (e.g., RITLAND 1989; EL-KASSABY and JAQUISH 1996) or by the number of different fathers involved (e.g., CAMPBELL 1998). In this context, pure half-sib and pure full-sib families represent the extreme alternatives of a continuum from uncorrelated to totally correlated mating events (e.g., polyads of mimosoid legumes and tropical figs; NASON et al. 1998). Correlated paternity can also be considered between maternal progeny arrays, where it can be expressed by the relative proportions of (paternal) half-sibs and non-sibs.

In plant populations, correlated paternity is important for several reasons. First, it is of evolutionary significance as it affects the genetic relatedness between maternal sibs and hence the response to selection when sibs are competing for maternal resources during seed maturation, affecting the effectiveness of selective fruit or embryo abortion, as well as resource allocation to each sex (Charnov 1982). Under limited seed dispersal, where interacting individuals are likely sibs, it may also act on the type of competitive interactions involved (e.g., kin selection; HAMILTON 1964; SCHUSTER and MITTON 1991; ROUSSET and BILLIARD 2000), the average fitness of competing siblings (YOUNG 1981; SCHMITT and EHRHARDT 1987; KARRON and MARSHALL 1990, 1993), or the success of mating events between nearby individuals when inbreeding depression or self-incompatibility occurs. Second, together with the outcrossing rate, the pattern of correlated mating is a key parameter of the mating system (RITLAND 1988, 2002) and can provide valuable information on pollination biology because it depends on a set of biological factors related in particular to floral biology, phenology, flowering intensity, pollinator behavior, pollen dispersal distances, and pollen competition. For example, several studies investigating correlated mating in a hierarchical fashion, distinguishing maternal sibs within and among flowers or inflorescences, gathered insightful information on the way pollen was brought on flowers (e.g., SCHOEN 1985; RITLAND 1989; MORGAN and BARRETT 1990; MUONA et al. 1991; SAMPSON 1998). Variation in pollen viability among pollen donors may result in male gametophyte competition (NIKKANEN et al. 2000) and, consequently, affects patterns of correlated mating in successfully developed seeds. …

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