Megalopta Genalis Research Articles

Survival and productivity benefits to social nesting in the sweat bee Megalopta genalis (Hymenoptera: Halictidae)

Facultatively solitary and eusocial species allow for direct tests of the benefits of group living. We used the facultatively social sweat bee Megalopta genalis to test several benefits of group living. We surveyed natural nests modified for observation in the field weekly for 5 weeks in 2003. First, we demonstrate that social and solitary nesting are alternative behaviors, rather than different points on one developmental trajectory. Next, we show that solitary nests suffered significantly higher rates of nest failure than did social nests. Nest failure apparently resulted from solitary foundress mortality and subsequent brood orphanage. Social nests had significantly higher productivity, measured as new brood cells provisioned during the study, than did solitary nests. After accounting for nest failures, per capita productivity did not change with group size. Our results support key predictions of Assured Fitness Return models, suggesting such indirect fitness benefits favor eusocial nesting in M. genalis. We compared field collections of natural nests to our observation nest data to show that without accounting for nest failures, M. genalis appear to suffer a per capita productivity decrease with increasing group size. Calculating per capita productivity from collected nests without accounting for the differential probabilities of survival across group sizes leads to an overestimate of solitary nest productivity.

Ocellar optics in nocturnal and diurnal bees and wasps

Nocturnal bees, wasps and ants have considerably larger ocelli than their diurnal relatives, suggesting an active role in vision at night. In a first step to understanding what this role might be, the morphology and physiological optics of ocelli were investigated in three tropical rainforest species – the nocturnal sweat bee Megalopta genalis, the nocturnal paper wasp Apoica pallens and the diurnal paper wasp Polistes occidentalis – using hanging-drop techniques and standard histological methods. Ocellar image quality, in addition to lens focal length and back focal distance, was determined in all three species. During flight, the ocellar receptive fields of both nocturnal species are centred very dorsally, possibly in order to maximise sensitivity to the narrow dorsal field of light that enters through gaps in the rainforest canopy. Since all ocelli investigated had a slightly oval shape, images were found to be astigmatic: images formed by the major axis of the ocellus were located further from the proximal surface of the lens than images formed by the minor axis. Despite being astigmatic, images formed at either focal plane were reasonably sharp in all ocelli investigated. When compared to the position of the retina below the lens, measurements of back focal distance reveal that the ocelli of Megalopta are highly underfocused and unable to resolve spatial detail. This together with their very large and tightly packed rhabdoms suggests a role in making sensitive measurements of ambient light intensity. In contrast, the ocelli of the two wasps form images near the proximal boundary of the retina, suggesting the potential for modest resolving power. In light of these results, possible roles for ocelli in nocturnal bees and wasps are discussed, including the hypothesis that they might be involved in nocturnal homing and navigation, using two main cues: the spatial pattern of bright patches of daylight visible through the rainforest canopy, and compass information obtained from polarised skylight (from the setting sun or the moon) that penetrates these patches.

Social and ecological contexts of trophallaxis in facultatively social sweat bees, Megalopta genalis and M. ecuadoria (Hymenoptera, Halictidae)

Exchange of liquid food among adults (trophallaxis) is documented for the first time in New World sweat bees (Halictinae). Megalopta genalis and M. ecuadoria are facultatively social, and in social groups foragers regularly give food to the oldest resident female bee, which dominates social interactions. In turn, the oldest resident sometimes re-distributes this food, and shares it with younger foragers. Food is sometimes offered freely, but often the dominant bee exhibits escalating aggressive behavior until she is fed, whereupon she immediately ceases to be aggressive. The occurrence of trophallaxis in a species with mass-provisioned larvae provides an opportunity to examine the ritualization of social behavior. Trophallaxis also increases survivorship of males and females by almost 50% under experimental conditions, suggesting the behavior is also important in ecological contexts.

Visual summation in night-flying sweat bees: A theoretical study

Bees are predominantly diurnal; only a few groups fly at night. An evolutionary limitation that bees must overcome to inhabit dim environments is their eye type: bees possess apposition compound eyes, which are poorly suited to vision in dim light. Here, we theoretically examine how nocturnal bees Megalopta genalis fly at light levels usually reserved for insects bearing more sensitive superposition eyes. We find that neural summation should greatly increase M. genalis’s visual reliability. Predicted spatial summation closely matches the morphology of laminal neurons believed to mediate such summation. Improved reliability costs acuity, but dark adapted bees already suffer optical blurring, and summation further degrades vision only slightly.

Light intensity limits foraging activity in nocturnal and crepuscular bees

A crepuscular or nocturnal lifestyle has evolved in bees several times independently, probably to explore rewarding pollen sources without competition and to minimize predation and nest parasites. Despite these obvious advantages, only few bee species are nocturnal. Here we show that the sensitivity of the bee apposition eye is a major factor limiting the ability to forage in dim light. We present data on eye size, foraging times, and light levels for Megalopta genalis (Augochlorini, Halictidae) in Panama, and Lasioglossum (Sphecodogastra) sp. (Halictini, Halictidae) in Utah, USA. M. genalis females forage exclusively during twilight, but as a result of dim light levels in the rain forest, they are adapted to extremely low intensities. The likely factor limiting their foraging activity is finding their nest entrance on return from a foraging trip. The lowest light intensity at which they can do this, both in the morning and the evening, is 0.0001 cd m � 2 . Therefore, they leave the nest at dimmer light levels in the morning than in the evening. Lasioglossum (Sphecodogastra) foraging is limited by light intensity in the evening, but probably by temperature in the morning in the temperate climate of Utah. We propose that the evolution of nocturnality in bees was favored by the large

The Development of Neuronal Morphology in Insects

Neurons are highly polarized cells with some regions specified for information input--typically the dendrites--and others specialized for information output--the axons. By extending to a specific location and branching in a specific manner, the processes of neurons determine at a fundamental level how the nervous system is wired to produce behavior. Recent studies suggest that relatively small changes in neuronal morphology could conceivably contribute to striking behavioral distinctions between invertebrate species. We review recent data that begin to shed light on how neurons extend dendrites to their targets and acquire their particular branching morphologies, drawing primarily on data from genetic model organisms. We speculate about how and why the actions of these genes might facilitate the diversification of dendritic morphology.

A neural network to improve dim-light vision? Dendritic fields of first-order interneurons in the nocturnal bee Megalopta genalis

Using the combined Golgi-electron microscopy technique, we have determined the three-dimensional dendritic fields of the short visual fibres (svf 1-3) and first-order interneurons or L-fibres (L1-4) within the first optic ganglion (lamina) of the nocturnal bee Megalopta genalis. Serial cross sections have revealed that the svf type 2 branches into one adjacent neural unit (cartridge) in layer A, the most distal of the three lamina layers A, B and C. All L-fibres, except L1-a, exhibit wide lateral branching into several neighbouring cartridges. L1-b shows a dendritic field of seven cartridges in layers A and C, dendrites of L2 target 13 cartridges in layer A, L3 branches over a total of 12 cartridges in layer A and three in layer C and L4 has the largest dendritic field size of 18 cartridges in layer C. The number of cartridges reached by the respective L-fibres is distinctly greater in the nocturnal bee than in the worker honeybee and is larger than could be estimated from our previous Golgi-light microscopy study. The extreme dorso-ventrally oriented dendritic field of L4 in M. genalis may, in addition to its potential role in spatial summation, be involved in edge detection. Thus, we have shown that the amount of lateral spreading present in the lamina provides the anatomical basis for the required spatial summation. Theoretical and future physiological work should further elucidate the roles that this lateral spreading plays to improve dim-light vision in nocturnal insects.

The evolution of nocturnal behaviour in sweat bees, Megalopta genalis and M. ecuadoria (Hymenoptera: Halictidae): an escape from competitors and enemies?

Evolutionary transitions to dim-light foraging (predawn matinal, crepuscular, nocturnal) have occurred repeatedly in bees, and may be associated with an escape from enemies or competitors. To date, however, little information has been available to test these hypotheses. Here we provide the first detailed information on the nesting behaviour of two species of Neotropical, nocturnal sweat bees, Megalopta genalis and M. ecuadoria (Hymenoptera: Halictidae). Females are facultatively social or solitary, and construct nests in dead wood. Nocturnal foraging behaviour is bimodal. Bees began foraging after sunset (∼18:30 h) and ceased foraging approximately 1 h later even though nocturnal flowers with pollen were still abundant; a second foraging bout occurred in the predawn morning, which began at ∼04:45 h and ended around sunrise (∼06:15 h) when diurnal-blooming flowers were abundant. Bees are capable of controlled flight in full light. They utilized pollen from both canopy and understory plant species, which have diurnal or nocturnal pollen anthesis. Megalopta nests are attacked by generalist predators such as ants, as well as the endoparasitic fly Melaloncha sp. nov. (Phoridae), the beetle Macrosaigon gracilis (Rhipophoridae), the parasitic wasp Lophostigma cincta (Mutillidae), and the brood parasite Megalopta byroni (Halictidae). Overall nest survivorship rates were comparable to those for diurnal relatives, but rates of cell parasitism for Megalopta (< < 5%) were substantially lower than they are for day-flying relatives, offering some support for the hypothesis that the evolution of nocturnal behaviour enables escape from natural enemies. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 377–387.

A review of deviant phenotypes in bees in relation to brood parasitism, and a gynandromorph of Megalopta genalis (Hymenoptera: Halictidae)

We review the occurrence of gynandromorphy in 64 species of bee, and describe the abnormal traits as deviations from the male or female wild-type. Pheno-deviants occur at approximately equal frequency among the main body regions (head, thorax, metasoma). Cross-sex expression of character states occur more often among females (i.e. deviant expression of male-like traits) than among males (i.e. deviant expression of female-like traits). Such pathologies demonstrate how developmental switch mechanisms might generate novel structural traits similar to those expressed as a syndrome of brood parasitic traits. We also describe the first known gynandromorphic bee in the tribe Augochlorini, a specimen of the nocturnal bee, Megalopta genalis.

Retinal and optical adaptations for nocturnal vision in the halictid bee Megalopta genalis.

The apposition compound eye of a nocturnal bee, the halictid Megalopta genalis, is described for the first time. Compared to the compound eye of the worker honeybee Apis mellifera and the diurnal halictid bee Lasioglossum leucozonium, the eye of M. genalis shows specific retinal and optical adaptations for vision in dim light. The major anatomical adaptations within the eye of the nocturnal bee are (1) nearly twofold larger ommatidial facets and (2) a 4-5 times wider rhabdom diameter than found in the diurnal bees studied. Optically, the apposition eye of M. genalis is 27 times more sensitive to light than the eyes of the diurnal bees. This increased optical sensitivity represents a clear optical adaptation to low light intensities. Although this unique nocturnal apposition eye has a greatly improved ability to catch light, a 27-fold increase in sensitivity alone cannot account for nocturnal vision at light intensities that are 8 log units dimmer than during daytime. New evidence suggests that additional neuronal spatial summation within the first optic ganglion, the lamina, is involved.

A review of deviant phenotypes in bees in relation to brood parasitism, and a gynandromorph of Megalopta genalis (Hymenoptera: Halictidae)

A review of deviant phenotypes in bees in relation to brood parasitism, and a gynandromorph of Megalopta genalis (Hymenoptera: Halictidae)

Assured fitness returns favor sociality in a mass-provisioning sweat bee, Megalopta genalis (Hymenoptera: Halictidae)

Assured fitness returns models for the evolution of sociality emphasize the selective value of ensuring that offspring receive adequate parental care to reach maturity. If a member of a social group dies, it can accrue returns on investment in offspring through the efforts of surviving social partners. We provide evidence that in the mass-provisioning, facultatively social sweat bee Megalopta genalis, adult presence in the nest throughout brood development provides protection from ant predation. Nests with adults present were well protected, and brood in nests with adults removed suffered higher predation. Females in observation nests showed effective defensive behavior against experimentally introduced ants, and bees in natural nests repulsed naturally occurring ant raids. Megalopta nest architecture and behavior are such that the brood of several cooperating females can be defended with little additional cost relative to solitary nesting. The benefits of cooperative defense may favor group living in mass provisioning bees. Our observations and experiments suggest that parental care throughout brood development can be adaptive in mass provisioning species, supporting the predictions of assured fitness returns models.

Unmatedness and the Evolution of Eusociality

Previous articleNext article No AccessNotes and CommentsUnmatedness and the Evolution of EusocialityH. C. J. Godfray and A. GrafenH. C. J. Godfray Search for more articles by this author and A. Grafen Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 131, Number 2Feb., 1988 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/284791 Views: 17Total views on this site Citations: 24Citations are reported from Crossref Copyright 1988 The University of ChicagoPDF download Crossref reports the following articles citing this article:Adam R. Smith, Karen M. Kapheim, Callum J. Kingwell, William T. Wcislo A split sex ratio in solitary and social nests of a facultatively social bee, Biology Letters 15, no.44 (Apr 2019): 20180740.https://doi.org/10.1098/rsbl.2018.0740Rebecca M. Dew, Simon M. Tierney, Michael P. Schwarz Lack of ovarian skew in an allodapine bee and the evolution of casteless social behaviour, Ethology Ecology & Evolution 30, no.11 (Jun 2017): 51–69.https://doi.org/10.1080/03949370.2017.1313784Petri Rautiala, Heikki Helanterä, Mikael Puurtinen The evolutionary dynamics of adaptive virginity, sex-allocation, and altruistic helping in haplodiploid animals, Evolution 72, no.11 (Dec 2017): 30–38.https://doi.org/10.1111/evo.13399Petri Rautiala, Heikki Helanterä, and Mikael Puurtinen Unmatedness Promotes the Evolution of Helping More in Diplodiploids than in Haplodiploids., The American Naturalist 184, no.33 (Jul 2015): 318–325.https://doi.org/10.1086/677309Andy Gardner Dynamics of sex ratio and female unmatedness under haplodiploidy, Ecology and Evolution 4, no.99 (Apr 2014): 1623–1628.https://doi.org/10.1002/ece3.1045Karen M. Kapheim, Adam R. Smith, Peter Nonacs, William T. Wcislo, Robert K. Wayne Foundress polyphenism and the origins of eusociality in a facultatively eusocial sweat bee, Megalopta genalis (Halictidae), Behavioral Ecology and Sociobiology 67, no.22 (Nov 2012): 331–340.https://doi.org/10.1007/s00265-012-1453-xAndy Gardner, João Alpedrinha, and Stuart A. West Haplodiploidy and the Evolution of Eusociality: Split Sex Ratios., The American Naturalist 179, no.22 (Jul 2015): 240–256.https://doi.org/10.1086/663683Jacobus J. Boomsma Lifetime monogamy and the evolution of eusociality, Philosophical Transactions of the Royal Society B: Biological Sciences 364, no.15331533 (Nov 2009): 3191–3207.https://doi.org/10.1098/rstb.2009.0101Thomas W. Chapman, Bernard J. Crespi, Scott P. 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Nocturnal Bee Abundance and Seasonal Bee Activity in a Panamanian Forest

Bees were monitored weekly for 7 yr at light traps in the tropical monsoon forest of Barro Colorado Island. Fifty species and 17 genera were recorded, including nocturnal Megalopta and crepuscular Rhinetula (Halictidae) and Ptiloglossa (Colletidae). Twenty—eight native meliponines and African Apis mellifera in traps increased the known resident highly social bees to 32 species. Most of the 11,860 bees were Megalopta; these species were present throughout the year, as were Rhinetula and Ptiloglossa. Abundance of Megalopta was lowest during the dry season; this was its only consistent seasonality. Peak abundance occurred at various times during dry—to—wet—season transition and in the first half and the end of the wet season. Centris and Epicharis, large, solitary anthrophorid bees, were present in the early wet season and absent in the late wet season and most of the dry season. The highly social bee Trigona aff. cupira was aseasonal but had abundance peaks during all but the mid—to—late wet season. Megalopta genalis abundance and M. ecuadoria abundance were highly positively correlated within years, and weekly correlated with abundances of other bees. Pairwise correlations between years were low for each Megalopta species and for combined bees of other genera. A singularly large catch of Megalopta genalis in 1978 corresponded to flowering of the monocarpic tree Tachigalia versicolor near light traps. Fluctuation of bee abundance at light traps probably indicates local flower availability for this species and, to a lesser extent, for the other bees. The data suggest large year—to—year variation in seasonal abundance of resources used by nocturnal bees and by bees in general, but are limited to indicating the presence or absence of most other bee species. The yearly variances in abundance of a stingless bee species and of Megalopta in Panama are comparable to those of eight temperate bumble bee species studied in England, but combined diurnal and crepuscular bee abundance is considerably less variable. The African honey bee arrived on Barro Colorado Island in mid—1982 and has produced no noticeable changes in abundance of other bees but has yet to reach its potential, numbers there; light—trap studies could provide perhaps the most reliable information on its impact.