Biology subjects

Sletvold, N.

Publications and source records attributed to Sletvold, N..

3 recordsLinked to original sources

bioRxiv2025

The role of secondary pollinators in the evolution of complex colour signals in a bimodal pollination system

Flower colour is recognized as a key trait influencing pollinator visitation and behaviour, evolved to match the sensory system of a particular pollinator group. However, some flowers combine colours associated with different pollinators, suggesting bimodal adaptation. The perennial herb Cyrtanthus obliquus produces red corollas with yellow tips and is pollinated by birds, but also by bees. To assess the role of the two pollinator categories in shaping selection on the bi-coloured corollas, we examined bee choices in arrays in which the colour signals of plants had been manipulated, and we quantified total as well as bird-mediated phenotypic selection on flower colour using both bird and bee visual models. Bees preferred flowers with a yellow signal over all-red flowers. The analysis of phenotypic selection indicated that both birds and bees influence net selection on flower colour, resulting in conflicting selection on the colour contrast between corolla and corolla tip. Our findings show that the optimal phenotype should depend on the relative importance of the two categories of pollinators in a given population, and are consistent with bimodal adaptation. This study fills an important gap by showing that secondary pollinators can contribute to selection on complex colour signals in angiosperm flowers.

evolutionary biology↗

bioRxiv2025

Do sun orchids mimic buzz-pollinated plants? An experimental test of the adaptive significance of false anthers

O_LIMimicry implies that an organism gains fitness by resembling a model species, and one example is rewardless plants that attract pollinators by resembling co-flowering species that provide rewards. While trait matching between mimic and model has been characterised in many cases of putative floral mimicry, few have demonstrated that resemblance is adaptive and dependent on model presence. C_LIO_LISun orchids (Thelymitra) are believed to mimic flowers of buzz-pollinated rewarding plants by displaying false anthers. To test the adaptive value of the false anthers we examined whether fruit production of T. crinita and T. macrophylla was reduced when anthers were experimentally removed or obscured, and whether the reduction was stronger when putative model plants were abundant. We also assessed visual flower similarity of both orchids and their putative model plants according to bee colour perception and identified shared pollinators and whether their behaviour on T. crinita was similar to that on co-flowering rewarding plants. C_LIO_LIFruit production of both sun orchids was strongly reduced (60-71%) by removal or painting of false anthers but was not affected by the abundance of model plants. Sun orchid flowers closely matched flower colour of co-flowering pollen-rewarding species, and T. crinita shared pollinators with the rewarding species. Visiting bees attempted to buzz and manipulate the false anther, with a behaviour similar to that observed on model plants. C_LIO_LIThe experimental results demonstrate that the false anther is an important adaptation to pollination in sun orchids. Striking visual flower similarity and shared pollinators between orchids and models suggest that sun orchids are pollinated by bees that mistake orchids for buzz-pollinated rewarding plants. The adaptive value of the false anther did not depend on model plant abundance in the local population, indicating that the relevant spatial scale is larger, or that the effects of the model species are weak in comparison to effects of other rewarding species, i.e., that magnet effects of nectar-rewarding species are dominating. C_LIO_LIFalse anthers are widespread in the genus Thelymitra, and this "mimicry trait" seems to represent an evolutionary novelty that offers unique opportunities to explore adaptations to pollination in deceptive plants. C_LI

ecology↗

bioRxiv2025

Nuances of floral mimicry in Queen of Sheba orchids

O_LIBackground and Aims Floral deception can range from finely tuned mimicry of specific rewarding plants (Batesian mimicry) to a general resemblance of the rewarding community (generalised food deception). We focused on two species in the deceptive Thelymitra variegata complex (Queen of Sheba orchids) to examine whether pollination is consistent with generalised food deception or with specific mimicry of co-flowering buzz-pollinated tinsel lilies (Calectasia spp.). C_LIO_LIMethods We assessed i) overlap in flower colour and scent between orchids, tinsel lilies, and other flowers in the rewarding community, ii) pollinator sharing between orchids, tinsel lilies and other species, and ii) quantified orchid reproductive success in relation to abundance of tinsel lilies and other rewarding species. C_LIO_LIKey Results We found that T. speciosa matches flower colour and scent of its co-flowering tinsel lily, C. gracilis, while T. porphyrosticta partly overlaps with co-flowering C. demarzii in both traits. The orchids and tinsel lilies shared flower visitors, and the only visitor observed to transfer orchid pollen was Anthoglossa plumata bee (Colletidae) that displayed a behaviour associated with buzz pollination. This species was also observed to buzz-pollinate tinsel lilies. In T. speciosa, fruit production increased with abundance of both tinsel lilies and other rewarding species with similar flower colour, suggesting a combination of mimicry and magnet effects. However, relationships were driven by a single population. There was no association between rewarding community and reproductive success in T. porphyrosticta. C_LIO_LIConclusions The results are partly consistent with mimicry towards the co-flowering tinsel lily for both orchids. Specific mimicry is strongly supported by a close resemblance involving multiple floral traits, and by bee behaviour associated with the buzz-pollinated model. However, this contrasts with the lack of consistent effects of tinsel lily abundance on orchid reproductive success. The findings further suggest that shared floral scent may reinforce visual similarity and highlight that scent may be important in food mimicry systems. More generally, the T. variegata complex offers an interesting system for studying nuances between specific mimicry and generalised deception. C_LI

ecology↗