Colour vision in nocturnal insects

The ability to see colour at night is known only from a handful of animals. First discovered in the elephant hawk moth Deilephila elpenor, nocturnal colour vision is now known from two other species of hawk moths, a single species of carpenter bee, a nocturnal gecko and two species of anurans. The reason for this rarity - particularly in vertebrates - is the immense challenge of achieving a sufficient visual signal-to-noise ratio to support colour discrimination in dim light. Although no less challenging for nocturnal insects, unique optical and neural adaptations permit reliable colour vision and colour constancy even in starlight. Using the well-studied Deilephila elpenor, we describe the visual light environment at night, the visual challenges that this environment imposes and the adaptations that have evolved to overcome them. We also explain the advantages of colour vision for nocturnal insects and its usefulness in discriminating night-opening flowers. Colour vision is probably widespread in nocturnal insects, particularly pollinators, where it is likely crucial for nocturnal pollination. This relatively poorly understood but vital ecosystem service is threatened from increasingly abundant and spectrally abnormal sources of anthropogenic light pollution, which can disrupt colour vision and thus the discrimination and pollination of flowers. This article is part of the theme issue 'Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods'

Data from: Behavioural responses vary with prey species in the social spider, Stegodyphus sarasinorum

Predators living in social groups often show consistent inter-individual differences in prey capture behaviour that may be linked to personality. Though personality predisposes individuals for certain behaviours, responses can also be influenced by context. Studies examining personality-dependent participation in prey capture have largely employed only one prey species, offering the predator no choice. In nature, predators encounter a range of prey species, therefore participation in or leading a prey capture event must also depend on prey attributes (for example, size and risk). In the social spider Stegodyphus sarasinorum, collective prey capture is mediated by personality types as a consequence of which some individuals are consistently more likely to attack. Here, we examined if an individual’s consistency to attack persisted within and between the two prey species (honeybees and grasshoppers), and if the same individuals attacked first with both prey species. Our results showed that inter-individual differences in attacking persisted within- and between the two prey species. Spiders showed greater participation in attacking grasshoppers relative to bees. Identities of first attackers were not the same for bees and grasshoppers. Spiders showed greater consistency over time in attacking bees relative to grasshoppers. Bees attracted fewer attackers than size-matched grasshoppers. These results suggest that greater task specialization may be necessary to successfully subdue bees. Spiders handled bees more cautiously, which is likely to explain the observed plasticity in attacking the two prey species. Thus, participation in prey capture in social spiders is influenced by the attributes of prey species

Spatial vision and visually guided behavior in apidae

The family Apidae, which is amongst the largest bee families, are important pollinators globally and have been well studied for their visual adaptations and visually guided behaviors. This review is a synthesis of what is known about their eyes and visual capabilities. There are many species-specific differences, however, the relationship between body size, eye size, resolution, and sensitivity shows common patterns. Salient differences between castes and sexes are evident in important visually guided behaviors such as nest defense and mate search. We highlight that Apis mellifera and Bombus terrestris are popular bee models employed in the majority of studies that have contributed immensely to our understanding vision in bees. However, other species, specifically the tropical and many non-social Apidae, merit further investigation for a better understanding of the influence of ecological conditions on the evolution of bee vision

Data from: Body condition and food shapes group dispersal but not solitary dispersal in a social spider

Dispersal is important for exploitation of new habitat and for outbreeding. A precondition for sociality in spiders is reduced dispersal propensity leading to largely inbred societies. Despite this, social spiders have been observed to disperse from natal colonies and form new or satellite colonies. Proximate factors shaping dispersal, inter-individual variation in dispersal propensities and any advantages accrued from dispersal remain obscure. In the social spider Stegodyphus sarasinorum, we distinguish two types of dispersal: 1) group dispersal in which groups of sub-adult spiders move to form adjacent satellite colonies that are connected to the natal retreat by a shared capture web and 2) solitary dispersal, where a single mated female disperses from the natal colony and can potentially establish a new independent colony. Using experimental colonies that varied in size and subjected to long-term differential food treatment, we show that individuals that participate in group dispersal have lower body condition than natal females. Well-fed colonies had more group dispersers compared to less-fed colonies. Body condition, food availability and colony size did not influence solitary dispersal. Interestingly, solitary dispersers suffered heavy mortality (~ 75%) likely due to predation, however survivors gained better body condition and higher fat reserves post-dispersal compared to natal females. We did not detect greater fitness (measured as clutch size and mean egg weight) in solitary dispersers. Finally, by following group dispersers and natal females, we found that both were equally likely to become solitary dispersers suggesting that solitary and group dispersal are two different dispersal strategies

Nocturnal pollination by the carpenter bee Xylocopa tenuiscapa (Apidae) and the effect of floral display on fruit set of Heterophragma quadriloculare (Bignoniaceae) in India.

We provide the first data on nocturnal pollination by bees. Heterophragma quadriloculare is a self-incompatible hermaphroditic tree solely pollinated at night by the carpenter bee Xylocopa (Mesotrichia) tenuiscapa Westwood, whose pollinating flights were lunar insensitive and unaffected by low nighttime temperatures (2-14°C). The number of carpenter bees visiting a tree per minute and the number of flowers visited per foraging bout were positively related to the size of the floral display. We found that floral display size was negatively related to fruit set but positively related to absolute fruit numbers. In pollen carryover experiments, cross-pollen did not travel far in sequences of nonemasculated flowers (up to the 4th flower), but traveled farther in emasculated flower sequences (up to the 15th flower) as evidenced by fruit set in these sequences. The relatively poor fruit set on trees with many open flowers may have resulted from deposition of self-pollen on touch-sensitive stigmas, which close on first contact. Because largegirth trees tend to have large floral displays, trees may increasingly realize a higher percentage of fitness through male rather than female function as they age. The steady-state flowering phenology of H quadriloculare may limit reduction in the female function compared to the cornucopia strategy of many other members of the Bignoniaceae and may also provide a reliable resource for X tenuiscapa

Nocturnal pollination by the carpenter bee xylocopa tenuiscapa (Apidae) and the effect of floral display on fruit set of heterophragma quadriloculare (Bignoniaceae) in India

We provide the first data on nocturnal pollination by bees. Heterophragma quadriloculare is a self-incompatible hermaphroditic tree solely pollinated at night by the carpenter bee Xylocopa (Mesotrichia) tenuiscapa Westwood, whose pollinating flights were lunar insensitive and unaffected by low nighttime temperatures (2-14°C). The number of carpenter bees visiting a tree per minute and the number of flowers visited per foraging bout were positively related to the size of the floral display. We found that floral display size was negatively related to fruit set but positively related to absolute fruit numbers. In pollen carryover experiments, cross-pollen did not travel far in sequences of non-emasculated flowers (up to the 4th flower), but traveled farther in emasculated flower sequences (up to the 15th flower) as evidenced by fruit set in these sequences. The relatively poor fruit set on trees with many open flowers may have resulted from deposition of self-pollen on touch-sensitive stigmas, which close on first contact. Because large-girth trees tend to have large floral displays, trees may increasingly realize a higher percentage of fitness through male rather than female function as they age. The steady-state flowering phenology of H. quadriloculare may limit reduction in the female function compared to the cornucopia strategy of many other members of the Bignoniaceae and may also provide a reliable resource for X. tenuiscapa

Influence of exploitation on population structure, spatial distribution and reproductive success of dioecious species in a fragmented cloud forest in India

The population structure of three dioecious species, Diospyros montana, Diospyros sylvatica and Garcinia talbotii was studied in a seasonal cloud forest in the Western Ghats of India. In an undisturbed, natural population of D. montana, female fecundity was not significantly influenced by distance to neighbours or by flower numbers on neighbours. In the same population fruit set was also unrelated to the angular dispersion of neighbours. On the other hand, in an altered population of this species in which conspecifics are extremely isolated due to human activities, insect visitation and fruit set were strongly and negatively correlated with distance to the nearest male. Moreover, the number of insects and fruit set in the natural population were significantly higher in the natural population than in the altered population. In the natural population, trees of large girth produced larger numbers of flowers in both sexes and females which produced larger numbers of flowers, also produced more fruits and fruit set (fruits/flower). In the altered population, fruit numbers and fruit set in female trees were unrelated to the flower numbers, which is possibly due to pollination limitation as a result of inadequate pollinator visits at female trees. Sex ratios were male-biased (3.7:1) in the natural population and female-biased (1:2) in the altered population of D. montana, as well as in G. talbotii (1:3.8) and D. sylvatica (1:12.2) populations where the lower girth classes are mainly cut. The girth class distribution of G. talbotii and D. sylvatica populations was skewed towards larger girths suggesting that future recruitment will be severely affected

Dispersal in S. sarasinorum

The data-set consists of body measurements, clutch size and egg weights of social spiders. There is information about the effect of food and colony size influencing dispersal tendencies