Alessandro Fisogni

Reproductive ecology in the endemic Primula apennina Widmer (Primulaceae)

Abstract Disassortative mating in distylous self-incompatible species should result in the equilibrium of morph types in natural populations. Deviation from isoplethy may affect pollen transfer, and in isolated populations it could lead to Allee effect and genetic drift. Pollen limitation has been found to occur in several distylous species, for which mating opportunities are actually reduced to half population. In this study, we investigated the reproductive features and pollination ecology of the narrow endemic Primula apennina. We recorded equilibrium of morph frequencies in the studied population, reflecting the comparable fecundity found in the two morphs. Long-styled flowers produce more pollen grains of smaller size than short-styled ones: we hypothesize that in thrum flowers, pollen is more easily removed by the insect pollinator Macroglossum stellatarum, resulting in equal pollen amounts carried to both short styles and long styles. This lower pollen transfer efficiency from long-styled to short-styled flowers is also reflected in legitimate pollen–ovule ratio values. Despite results show no evidence of imminent threats to population persistence at study site, the strict dependence on one or very few pollinator species, and ecological traits, may increase extinction risks in the long-term period.

Biosystematic studies on the mountain plant Gentiana lutea L. reveal variability in reproductive traits among subspecies

Background: Taxonomic analysis provides a basic understanding for taxon identification and contributes to preliminary information for several branches of applied biology, while studies on reproductive strategies and plant fitness are essential to interpret population status and dynamics. Aims: We tested the reliability of diagnostic characters for identification and to characterise sexual resource allocation, the breeding system and seed predation among subspecies of Gentiana lutea. Methods: We analysed morphological characters in 70 herbarium specimens. In five natural populations we counted pollen and ovule numbers, assessed reproductive output after pollination treatments and evaluated pre-dispersal predation. Results: Taxonomic traits previously indicated as diagnostic were not sufficient to discriminate among subspecies. The pollen number and pollen:ovule (P:O) ratio varied strongly among subspecies; self-pollinated flowers produced a significantly lower number of seeds than open-pollinated flowers. Retention of empty fruits and high levels of pre-dispersal seed predation were observed in every case. Conclusions: The variation of P:O ratios among subspecies suggests different efficiency in pollen transfer. The species is self-compatible, nevertheless all subspecies require pollen vectors to enhance cross pollination and viable seed production. Fruit retention may have evolved as a strategy to reduce predation, ensuring higher plant fitness.

All in an afternoon: mixed breeding system in one-day lasting flowers of Hypericum elodes L. (Hypericaceae)

Knowledge about mixed mating systems can improve our understanding of the evolutionary dynamics of reproductive systems. Here we report a study of the floral and reproductive biology of Hypericum elodes, an Atlantic-European soft-water pools specialist which shows a floral architecture consistent with both self- and cross-pollination. Controlled pollination experiments were performed in a natural population during three consecutive years. Marked flowers were monitored until fruit production, and laboratory germination experiments were conducted with the seeds produced. Plants were self-compatible (SCI>0.75), however, compared with selfing, cross-pollination enhanced fruit-set, seed-set and seedling growth, but not seed germination. Inbreeding depression (δ) was mild in the pre-dispersal stages (δ = 0.22 for fruit set, 0.18 for seed set and 0.13 for seed mass), low for germination percentage (δ = 0.003) and mild for seedling growth (δ = 0.23). The breeding system of H. elodes promotes outcrossing and assures reproductive success by means of competitive autogamy. Our results suggest a mixed mating strategy for the studied population, characterized by mild inbreeding depression (cumulative δ = 0.57), highlighting the benefit of this reproductive mode in unpredictable habitat, as the typical shallow-water meadows where H. elodes grows.

Effects of queen mating status, pre-diapause weight and pupae’s sex on colony initiation in small-scale rearing of Bombus terrestris

Diapause control and colony initiation are among the major problems encountered in the rearing of bumble bee colonies in small-scale rearing. In this study, we used Bombus terrestris queens obtained from commercial colonies to investigate (1) the diapause survival in virgin and mated queens, (2) the diapause and colony initiation performance of mated bumble bee queens in relation to the pre-diapause weight and (3) the effect of pupae’s sex on colony initiation. We found that diapause survival is negatively affected by mating and by the low pre-diapause weight, but first egg deposition and development of the first adult worker were delayed in heavy queens. We found no significant differences in the egg-laying success in relation to pupae’s sex; however, queens stimulated with queen pupae laid more eggs per cell and developed a first brood larger than those stimulated with male pupae. Our results can be useful in small-scale rearing, including the rearing of wild queens for conservation purposes.

Different reproductive strategies and their possible relation to inbreeding risk in the bumble bee Bombus terrestris

In many species, inbreeding avoidance mechanisms prevent mating between close relatives, but these mechanisms are poorly studied in bumble bees. The probability of inbred matings within a colony in eusocial insects may depend on the timing of gyne and male emergence and on their sex ratio. In this study, we compared the development of 35 colonies of the bumble bee Bombus terrestris from founding to the emergence of the last gyne, and we investigated the probability of inbred mating in colonies with fertile newborn gynes and males. We calculated a novel colony inbreeding risk index (IRI), which considers the overlap period between fertile gynes and males, their numbers, and the colony sex ratio. We found that the IRI values were strictly correlated with the time elapsed between the gyne point and the switch point (i.e., from the moment of deposition of the first diploid egg that produces a gyne to the first haploid egg). We separated the colonies into two groups based on the mean value of the IRI: colonies with low IRI produced more gynes (93.8 ± 9.4), for a longer period (32.1 ± 1.8 days) and with a lower percentage of overlapped gynes (69 ± 5%) than colonies with high IRI (57.1 ± 21 gynes, 23.3 ± 2.9 days, and 100% overlapped gynes, respectively). A low IRI is connected to a reduced risk of inbred mating, while colonies with a high IRI may be advantaged in conditions of isolation, in case of the absence of non-related reproducers. Inbreeding risk index proved to be a good indicator of the colony reproductive strategy.

Pollen load diversity and foraging niche overlap in a pollinator community of the rare Dictamnus albus L.

Bees collect pollen as an important resource for offspring development while acting as pollen vectors for the plants visited. Foraging preferences of pollinators together with plant species availability shape the web of interactions at the local scale. In this study, we focused on the bee pollinator community of a population of the rare protected perennial herb Dictamnus albus, with the aim to characterise the pollen preferences and the foraging niche overlap among species through time. Bees were sampled during four consecutive years in a natural population of D. albus, throughout the blooming period of the plant species. We performed an analysis of insect pollen loads to investigate the interactions with the study species and the co-flowering plants in the area, and to evaluate the degree of foraging overlap among pollinators. Over the study years, all bee species showed a high fidelity to D. albus (60–80%), even if some taxa preferentially collected pollen from other flowering species. The foraging niche overlap in the pollinator community decreased together with an increased diversity of co-flowering plant species. The results obtained indicate that bees preferentially forage on D. albus in the studied area, but that co-flowering species contribute to complement their diet and likely reduce competition for foraging resources. It appears therefore important to maintain a high diversity of co-flowering plants to preserve the diversity in the studied pollinator community of D. albus.