Disentangling the causes of heterogeneity in male fecundity in gynodioecious Beta vulgaris ssp. maritima

Diallelic self-incompatibility is the main determinant of fertilization patterns in olive orchards

Self-incompatibility (SI) in flowering plants potentially represents a major obstacle for sexual reproduction, especially when the number of S-alleles is low. The situation is extreme in the commercially important olive tree, where in vitro pollination assays suggested the existence of a diallelic SI (DSI) system involving only two groups (G1 and G2). Varieties belonging to the same SI group cannot fertilize each other, such that successful fruit production is predicted to require pollination between varieties of different groups. To test this prediction, we explored the extent to which the DSI system determines fertilization patterns under field conditions. One hundred and seventeen olive cultivars were first genotyped using 10 highly polymorphic dinucleotide Simple Sequence Repeat (SSR) markers to ascertain varietal identity. Cultivars were then phenotyped through controlled pollination tests to assign each of them to one of the two SI groups. We then collected and genotyped 1440 open pollinated embryos from five different orchards constituted of seven local cultivars with known group of incompatibility groups. Embryos genotype information were used: (i) to assign embryos to the most likely pollen donor genotype in the neighbourhood using paternity analysis, and (ii) to compare the composition of the pollen cloud genetic among recipient trees in the five sites. The paternity analysis showed that the DSI system is the main determinant of fertilization success under field open pollination conditions: G1 cultivars sired seeds exclusively on G2 cultivars, and reciprocally. No self-fertilization events were observed. Our results demonstrate that DSI is a potent force determining pollination success among varieties within olive orchards used for production. They have the potential to improve management practices by guiding the selection of compatible varieties to avoid planting orchards containing sets of varieties with strongly unbalanced SI groups, as these would lead to suboptimal olive production.

Seed germination of gynodioecious species: theoretical considerations and a comparison of females and hermaphrodites

Better seed germination of females than of hermaphrodites is not a major contributor to the greater geometric lifetime fitness that females require to be maintained in a gynodioecious population. Gynodioecy is a sexually dimorphic breeding system in which females (F, male sterile) and hermaphrodites (H) coexist in the same population. For plants with nuclear (biparental) inheritance of male sterility, theory predicts that except when the product of selfing rate (s) and inbreeding depression (δ) in H is high (sδ > 0.50), F must compensate (female advantage) for the loss of gene transmission via pollen production by producing more or higher-quality offspring than H to be maintained in the population. For species with cytoplasmic (maternal) inheritance of male sterility, the female requires only a small compensation in seed production or some other offspring fitness trait to persist. Reallocation to seeds of resources saved by loss of pollen production is expected to increase the quantity (number) and/or quality (mass, germinability) of seeds produced by F, thus compensating for the lack of pollen production. The primary aim of our study was to compare seed germination of F and H via a literature review. Based on theoretical considerations, we hypothesized that seeds of F should germinate better or equally as well as those of H. We found that of 235 case studies for 47 species F_germ > H_germ in 48.1%, F_germ = H_germ in 38.3% and F_germ < H_germ in 13.6%. Our results are very similar to those of a previously published meta-analysis that included germination of F and H for 12 species. For 162 cases on seed size, F > H in 29.0%, F = H in 63.6% and F < H in 7.4%. Since [(F_germ > H_germ) < (F_germ ≤ H_germ)] and [(F_seedsize > H_seedsize) < (F_seedsize ≤ H_seedsize)], these results suggest that seed quality is not a major fitness component of female advantage.

Phenological match drives pollen-mediated gene flow in a temporally dimorphic tree

Variation in flowering phenology is common in natural populations, and is expected to be, together with inter-mate distance, an important driver of effective pollen dispersal. In populations composed of plants with temporally separated sexual phases (i.e. dichogamous or heterodichogamous populations), pollen-mediated gene flow is assumed to reflect phenological overlap between complementary sexual phases. In this study, we conducted paternity analyses to test this hypothesis in the temporally dimorphic tree Acer opalus. We performed spatially explicit analyses based on categorical and fractional paternity assignment, and included tree size, pair-wise genetic relatedness and morph type as additional predictors. Because differences between morphs in flowering phenology may also influence pollination distances, we modelled separate pollen dispersal kernels for the two morphs. Extended phenological overlap between male and female phases (mainly associated with inter-morph crosses) resulted in higher siring success after accounting for the effects of genetic relatedness, morph type and tree size, while reduced phenological overlap (mainly associated with intra-morph crosses) resulted in longer pollination distances achieved. Siring success also increased in larger trees. Mating patterns could not be predicted by phenology alone. However, as heterogeneity in flowering phenology was the single morph-specific predictor of siring success, it is expected to be key in maintaining the temporal dimorphism in A. opalus, by promoting not only a prevalent pattern of inter-morph mating, but also long-distance pollination resulting from intra-morph mating events.

Size advantage for male function and size-dependent sex allocation in Ambrosia artemisiifolia, a wind-pollinated plant

In wind‐pollinated plants, male‐biased sex allocation is often positively associated with plant size and height. However, effects of size (biomass or reproductive investment) and height were not separated in most previous studies. Here, using experimental populations of monoecious plants, Ambrosia altemisiifolia, we examined (1) how male and female reproductive investments (MRI and FRI) change with biomass and height, (2) how MRI and height affect male reproductive success (MRS) and pollen dispersal, and (3) how height affects seed production. Pollen dispersal kernel and selection gradients on MRS were estimated by 2,102 seeds using six microsatellite markers. First, MRI increased with height, but FRI did not, suggesting that sex allocation is more male‐biased with increasing plant height. On the other hand, both MRI and FRI increased with biomass but often more greatly for FRI, and consequently, sex allocation was often female‐biased with biomass. Second, MRS increased with both height and MRI, the latter having the same or larger effect on MRS. Estimated pollen dispersal kernel was fat‐tailed, with the maximum distance between mates tending to increase with MRI but not with height. Third, the number of seeds did not increase with height. Those findings showed that the male‐biased sex allocation in taller plants of A. artemisiifolia is explained by a direct effect of height on MRS.

Individual quality and personality: bolder males are less fecund in the hermit crab Pagurus bernhardus

One explanation for animal personality is that different behavioural types derive from different life-history strategies. Highly productive individuals, with high growth rates and high fecundity, are assumed to live life at a fast pace showing high levels of boldness and risk taking, compared with less productive individuals. Here, we investigate among-individual differences in mean boldness (the inverse of the latency to recover from a startling stimulus) and in the consistency of boldness, in male hermit crabs in relation to two aspects of life-history investment. We assessed aerobic scope by measuring the concentration of the respiratory pigment haemocyanin, and we assessed fecundity by measuring spermatophore size. First, we found that individuals investing in large spermatophores also had high concentrations of haemocyanin. Using doubly hierarchical-generalized linear models to analyse longitudinal data on startle responses, we show that hermit crabs vary both in their mean response durations and in the consistency of their behaviour. Individual consistency was unrelated to haemocyanin concentration or spermatophore size, but mean startle response duration increased with spermatophore size. Thus, counter to expectations, it was the most risk-averse individuals, rather than the boldest and most risk prone, that were the most productive. We suggest that similar patterns should be present in other species, if the most productive individuals avoid risky behaviour.

Quantifying temporal isolation: a modelling approach assessing the effect of flowering time differences on crop-to-weed pollen flow in sunflower

Flowering time divergence can be a crucial component of reproductive isolation between sympatric populations, but few studies have quantified its actual contribution to the reduction of gene flow. In this study, we aimed at estimating pollen-mediated gene flow between cultivated sunflower and a weedy conspecific sunflower population growing in the same field and at quantifying, how it is affected by the weeds' flowering time. For that purpose, we extended an existing mating model by including a temporal distance (i.e. flowering time difference between potential parents) effect on mating probabilities. Using phenological and genotypic data gathered on the crop and on a sample of the weedy population and its offspring, we estimated an average hybridization rate of approximately 10%. This rate varied strongly from 30% on average for weeds flowering at the crop flowering peak to 0% when the crop finished flowering and was affected by the local density of weeds. Our result also suggested the occurrence of other factors limiting crop-to-weed gene flow. This level of gene flow and its dependence on flowering time might influence the evolutionary fate of weedy sunflower populations sympatric to their crop relative.