William T Wcislo

Smithsonian Tropical Research Institute, Ciudad de Panamá, Panamá, Panama

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Publications (91)308.95 Total impact

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    ABSTRACT: Social transmission and host developmental stage are thought to profoundly affect the structure of bacterial communities associated with honey bees and bumble bees, but these ideas have not been explored in other bee species. The halictid bees Megalopta centralis and Megalopta genalis exhibit intra-population social polymorphism, which we exploit to test whether bacterial communities differ by host social structure, developmental stage, or host species. We collected social and solitary Megalopta nests, and sampled bees and nest contents from all stages of host development. To survey these bacterial communities, we used 16S rRNA gene 454 pyrosequencing. We found no effect of social structure, but found differences by host species and developmental stage. Wolbachia prevalence differed between the two host species. Bacterial communities associated with different developmental stages appeared to be driven by environmentally acquired bacteria. A Lactobacillus kunkeei clade bacterium that is consistently associated with other bee species was dominant in pollen provisions and larval samples, but less abundant in mature larvae and pupae. Foraging adults appeared to often reacquire L. kunkeei clade bacteria, likely while foraging at flowers. Environmental transmission appears to be more important than social transmission for Megalopta bees at the cusp between social and solitary behavior. This article is protected by copyright. All rights reserved.
    FEMS Microbiology Ecology 03/2014; · 3.56 Impact Factor
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    ABSTRACT: Fungal symbionts that colonize leaf tissue asymptomatically (endophytes) can alter the foraging behaviour of leaf-cutting ants, and decrease the productivity of this herbivore's mutualistic fungal cultivar, Leucocoprinus gongylophorus. This negative effect of endophytes on the ant's cultivar could be the result of direct fungal–fungal interaction or indirect reductions in the quality of leaves, the cultivar's growth substratum. To test for the indirect effects, we measured in vitro growth rates of cultivars in media that contained sterilized leaf extracts from plants with high (Ehigh) and low (Elow) endophyte colonization. We found that, opposite to our expectations, cultivars grew significantly faster in Ehigh leaf extracts compared to Elow extracts. Our results suggest that endophyte-driven changes in leaf chemistry are a less likely explanation for the observed in vivo reduction in the ant's symbiotic fungal growth and imply that the effect of direct endophyte–cultivar interactions inside nests are potentially more important.
    Fungal Ecology 01/2014; 8:37–45. · 2.85 Impact Factor
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    ABSTRACT: Ant social parasites evolve adaptive relationships with their hosts. Theoretically, coevolution predicts strong selection to maximize fitness of the parasite that minimizes costs to its host, which potentially leads to the evolution of benign interactions. We studied the demographic and behavioral traits of the ant social parasite Megalomyrmex symmetochus (Solenopsidini), an agro-predator that feeds on larvae and fungal garden products of their host, Sericomyrmex amabilis (Attini). Based on demographic data from 15 parasitized colonies, the proportion of parasitic workers to those of the host is 1:2. Moreover, defensive prophylactic behaviors observed during infections with Metarhizium brunneum, a generalist entomopathogen, and Escovopsis, a specialized fungal garden parasite, showed that S. amabilis works extensively to remove and control fungal infections, in contrast to M. symmetochus. M. symmetochus, however, performed intraspecific allogrooming during infections with Escovopsis and M. brunneum, suggesting that they may recognize fungal pathogens and indirectly limit dispersion of spores. Our results indicate that M. symmetochus did not have a strong role in maintaining a hygienic nest.
    Insectes Sociaux 01/2014; 61(x):xxx-xxx. · 1.33 Impact Factor
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    ABSTRACT: Associative color learning has been demonstrated to be very poor using restrained European honey bees unless the antennae are amputated. Consequently, our understanding of proximate mechanisms in visual information processing is handicapped. Here we test learning performance of Africanized honey bees under restrained conditions with visual and olfactory stimulation using the proboscis extension response (PER) protocol. Restrained individuals were trained to learn an association between a color stimulus and a sugar-water reward. We evaluated performance for "absolute" learning (learned association between a stimulus and a reward) and "discriminant" learning (discrimination between two stimuli). Restrained Africanized honey bees (AHBs) readily learned the association of color stimulus for both blue and green LED stimuli in absolute and discriminatory learning tasks within 7 presentations, but not with violet as the rewarded color. Additionally, 24-hour memory improved considerably during the discrimination task, compared to absolute association (15%-55%). We found that antennal amputation was unnecessary and reduced performance in AHBs. Thus color learning can now be studied using the PER protocol with intact AHBs. This finding opens the way toward investigating visual and multimodal learning with application of neural techniques commonly used in restrained honey bees.
    Journal of Experimental Biology 09/2013; · 3.24 Impact Factor
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    ABSTRACT: Fungal symbionts that live asymptomatically inside plant tissues (endophytes) can influence plant-insect interactions. Recent work has shown that damage by leaf-cutting ants, a major Neotropical defoliator, is reduced to almost half in plants with high densities of endophytes. We investigated changes in the phenotype of leaves that could influence ants' behavior to result in the reduction of foliar damage. We produced cucumber seedlings with high and low densities of one common endophyte species, Colletotrichum tropicale. We used the leaves in bioassays and to compare chemical and physical leaf characteristics important for ants' food selection. Ants cut about one-third more area of cucumber leaves with lower densities of endophytes and removed c. 20% more paper disks impregnated with the extracts of those leaves compared with leaves and disks from plants hosting the fungus. Colletotrichum tropicale colonization did not cause detectable changes in the composition of volatile compounds, cuticular waxes, nutrients or leaf toughness. Our study shows that endophytes changed leaf chemistry and suggests that compounds with relative low volatility released after leaf wounding are a major factor influencing foraging decisions by ants when choosing between plants with low or high endophyte loads.
    New Phytologist 04/2013; 198(1):241-51. · 6.74 Impact Factor
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    ABSTRACT: The genus Mycocepurus is a phylogenetically basal attine ant, so studies of its biology may provide insight into the evolution of behaviours associated with fungus‐growing that characterize the tribe Attini. Mycocepurus smithii from Puerto Rico produces sexual females from July to September, but no males were observed in 2 years of observations, confirming previous observations elsewhere. Colonies were founded between July and August and most nests were haplometrotic (85% of 74 nests). After excavating a tunnel and small chamber, a foundress queen inserted her fore wings into the ceiling and used the wing surfaces as a platform on which the incipient fungal garden was grown. Foundresses foraged for substrate to grow the fungus garden. Growth of incipient colonies was slow: the first workers emerged 2–5 months after colony founding and, after 8 months, colonies contained on average only a single worker.
    Journal of Natural History 02/2013; 39:1735-1743. · 0.78 Impact Factor
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    ABSTRACT: Local environmental conditions can facilitate or preclude the development of eusocial colonies in insects that facultatively express behavioural-caste polyphenism. To explore how environmental variability relates to the expression of social behaviour, we collected 120 nests of the facultatively social sweat bee, Megalopta genalis (Halictidae: Augochlorini), along a nearly twofold rainfall gradient in central Panama. Brood rearing activity of bees in seasonal neotropical forests should track flowering phenologies, which are typically set by rainfall and phylogenetic patterns. Nests were collected at roughly similar times of year from three sites comprising wet, moist and dry lowland tropical forests. There were significant differences in ovarian development, brood production and body size across sites for some comparisons, but no effect on the proportion of social colonies collected at each site. Results show that phenotypes of M. genalis relevant to social behaviour (ovarian development, brood production, body size) may be responsive to variation in local environment over distances of <20 km.
    Insectes Sociaux 01/2013; 60(2):163-172. · 1.33 Impact Factor
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    ABSTRACT: The reproductive (queen) and nonreproductive (worker) castes of eusocial insect colonies are a classic example of insect polyphenism. A complementary polyphenism may also exist entirely among females in the reproductive caste. Although less studied, reproductive females may vary in behavior based on size-associated attributes leading to the production of daughter workers. We studied a bee with flexible social behavior, Megalopta genalis, to better understand the potential of this polyphenism to shape the social organization of bee colonies and, by extension, its role in the evolution of eusociality. Our experimental design reduced variation among nest foundresses in life history variables that could influence reproductive decisions, such as nesting quality and early adulthood experience. Within our study population, approximately one third of M. genalis nests were eusocial and the remaining nests never produced workers. Though they do not differ in survival, nest-founding females who do not attempt to produce workers (which we refer to as the solitary phenotype) are significantly smaller and become reproductive later than females who attempt to recruit workers (the social phenotype). Females with the social phenotype are more likely to produce additional broods but at a cost of having some of their first offspring become nonreproductive workers. The likelihood of eusocial organization varies with body size across females of the social phenotype. Thus, fitness consequences associated with size-based plasticity in foundress behavior has colony level effects on eusociality. The potential for size-based polyphenisms among reproductive females may be an important factor to consider in the evolutionary origins of eusociality.
    Behavioral Ecology and Sociobiology 01/2013; 67(2). · 2.75 Impact Factor
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    ABSTRACT: BACKGROUND: Previous work has shown that leaf-cutting ants prefer to cut leaf material with relatively low fungal endophyte content. This preference suggests that fungal endophytes exact a cost on the ants or on the development of their colonies. We hypothesized that endophytes may play a role in their host plants' defense against leaf-cutting ants. To measure the long-term cost to the ant colony of fungal endophytes in their forage material, we conducted a 20-week laboratory experiment to measure fungal garden development for colonies that foraged on leaves with low or high endophyte content. RESULTS: Colony mass and the fungal garden dry mass did not differ significantly between the low and high endophyte feeding treatments. There was, however, a marginally significant trend toward greater mass of fungal garden per ant worker in the low relative to the high endophyte treatment. This trend was driven by differences in the fungal garden mass per worker from the earliest samples, when leaf-cutting ants had been foraging on low or high endophyte leaf material for only 2 weeks. At two weeks of foraging, the mean fungal garden mass per worker was 77% greater for colonies foraging on leaves with low relative to high endophyte loads. CONCLUSIONS: Our data suggest that the cost of endophyte presence in ant forage material may be greatest to fungal colony development in its earliest stages, when there are few workers available to forage and to clean leaf material. This coincides with a period of high mortality for incipient colonies in the field. We discuss how the endophyte-leaf-cutter ant interaction may parallel constitutive defenses in plants, whereby endophytes reduce the rate of colony development when its risk of mortality is greatest.
    BMC Ecology 11/2012; 12(1):23.
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    ABSTRACT: The evolution of eusociality is hypothesized to have involved de-coupling parental care from reproduction mediated by changes in endocrine regulation. While data for obligately eusocial insects are consistent with this hypothesis, we lack information from species representative of the transition from solitary reproduction to eusociality. Here we report the first evidence for a link between endocrine processes and social behavior in a facultatively eusocial bee, Megalopta genalis (Halictidae). Using females that varied in social, reproductive, and ecological context, we measured juvenile hormone (JH), a major regulator of colony caste dynamics in other eusocial species. JH was low at adult emergence, but elevated after 10days in all nesting females. Females reared in cages with ad lib nutrition, however, did not elevate JH levels after 10days. All reproductive females had significantly more JH than all age-matched non-reproductive females, suggesting a gonadotropic function. Among females in established nests, JH was higher in queens than workers and solitary reproductives, suggesting a role for JH in social dominance. A lack of significant differences in JH between solitary reproductives and non-reproductive workers suggests that JH content reflects more than reproductive status. Our data support the hypothesis that endocrine modifications are involved in the evolutionary decoupling of reproductive and somatic effort in social insects. These are the first measurements of JH in a solitary-nesting hymenopteran, and the first to compare eusocial and solitary nesting individuals of the same species.
    Hormones and Behavior 09/2012; · 3.74 Impact Factor
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    ABSTRACT: Fungus-growing ants (Myrmicinae: Attini) live in an obligate symbiotic relationship with a fungus that they rear for food, but they can also use the fungal mycelium to cover their brood. We surveyed colonies from 20 species of fungus-growing ants and show that brood-covering behavior occurs in most species, but to varying degrees, and appears to have evolved shortly after the origin of fungus farming, but was partly or entirely abandoned in some genera. To understand the evolution of the trait we used quantitative phylogenetic analyses to test whether brood-covering behavior covaries among attine ant clades and with two hygienic traits that reduce risk of disease: mycelial brood cover did not correlate with mutualistic bacteria that the ants culture on their cuticles for their antibiotics, but there was a negative relationship between metapleural gland grooming and mycelial cover. A broader comparative survey showed that the pupae of many ant species have protective cocoons but that those in the subfamily Myrmicinae do not. We therefore evaluated the previously proposed hypothesis that mycelial covering of attine ant brood evolved to provide cocoon-like protection for the brood.
    Evolution 06/2012; 66(6):1966-75. · 4.86 Impact Factor
  • Andre J. Riveros, Marc A. Seid, William T. Wcislo
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    ABSTRACT: Highlights ► We examined sociality and brain size in nine genera of fungus-growing ants (Attini). ► Fungus-growing ants showed broad variation in colony size and social organization. ► Brain size varied among taxa in larger colonies and in more tightly knit societies. ► Larger colony size was associated with differential investment in olfactory brain centres. ► Analyses of social complexity using a scalogram yielded results similar to those using group size as a proxy.
    Animal Behaviour. 04/2012; 83(4):1043–1049.
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    ABSTRACT: Multipartner mutualisms have potentially complex dynamics, with compensatory responses when one partner is lost or relegated to a minor role. Fungus-growing ants (Attini) are mutualistic associates of basidiomycete fungi and antibiotic-producing actinomycete bacteria; the former are attacked by specialized fungi (Escovopsis) and diverse generalist microbes. Ants deploy biochemical defenses from bacteria and metapleural glands (MGs) and express different behaviors to control contaminants. We studied four Trachymyrmex species that differed in relative abundance of actinomycetes to understand interactions among antimicrobial tactics that are contingent on the nature of infection. MG grooming rate and actinomycete abundance were negatively correlated. The two species with high MG grooming rates or abundant actinomycetes made relatively little use of behavioral defenses. Conversely, the two species with relatively modest biochemical defenses relied heavily on behavior. Trade-offs suggest that related species can evolutionarily diverge to rely on different defense mechanisms against the same threat. Neither bacterial symbionts nor MG secretions thus appear to be essential for mounting defenses against the specialized pathogen Escovopsis, but reduced investment in one of these defense modes tends to increase investment in the other.
    The American Naturalist 02/2012; · 4.55 Impact Factor
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    ABSTRACT: As honey bee populations decline, interest in pathogenic and mutualistic relationships between bees and microorganisms has increased. Honey bees and bumble bees appear to have a simple intestinal bacterial fauna that includes acidophilic bacteria. Here, we explore the hypothesis that sweat bees can acquire acidophilic bacteria from the environment. To quantify bacterial communities associated with two species of North American and one species of Neotropical sweat bees, we conducted 16S rDNA amplicon 454 pyrosequencing of bacteria associated with the bees, their brood cells and their nests. Lactobacillus spp. were the most abundant bacteria in many, but not all, of the samples. To determine whether bee-associated lactobacilli can also be found in the environment, we reconstructed the phylogenetic relationships of the genus Lactobacillus. Previously described groups that associate with Bombus and Apis appeared relatively specific to these genera. Close relatives of several bacteria that have been isolated from flowers, however, were isolated from bees. Additionally, all three sweat bee species associated with lactobacilli related to flower-associated lactobacilli. These data suggest that there may be at least two different means by which bees acquire putative probiotics. Some lactobacilli appear specific to corbiculate apids, possibly because they are largely maternally inherited (vertically transmitted). Other lactobacilli, however, may be regularly acquired from environmental sources such as flowers. Sweat bee-associated lactobacilli were found to be abundant in the pollen and frass inside the nests of halictids, suggesting that they could play a role in suppressing the growth of moulds and other spoilage organisms.
    Molecular Ecology 02/2012; 21(7):1754-68. · 6.28 Impact Factor
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    ABSTRACT: 1. Spatial and temporal availability of pollen helps shape bee foraging behaviour and productivity, which has been studied in great detail at the landscape level, but never in a diverse tropical forest.2. To study the effect of spatio‐temporal variation in resource distribution on pollen use and productivity, we identified pollen from spatially explicit nest collections of two generalist sweat bees, Megalopta genalis Meade‐Waldo and M. centralis Friese, from Barro Colorado Island, Panama, a 50‐ha forest dynamics plot during the 2007 dry and early wet seasons. Pollen from nests collected in 1998–1999 without spatial information was also identified.3. Bees used pollen of at least 64 species; many of these occurred in only one collection. The 2007 collections contained pollen of 35 different species, but were dominated by five species, especially Hura crepitans L. and Pseudobombax septenatum (Jacq.) Dugand.4. Temporal availability, but not distance from nest, influenced flower use at a 50‐ha scale.5. Body size was not associated with minimum flight distance as inferred from pollen collections.6. Nest productivity and pollen diversity decreased from the dry to wet seasons, mirroring community‐level availability of floral resources.7. Results suggest that on a scale of 50 ha, bees are choosing certain host plant species regardless of distance from the nest, but adjusting foraging behaviour opportunistically based on the temporal availability of host flowers.
    Ecological Entomology 01/2012; · 1.95 Impact Factor
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    ABSTRACT: Parental care is rare in most lower vertebrates. By selecting optimal oviposition sites, however, mothers can realize some benefits often associated with parental care. We found three ovoid reptilian eggs within a mature nest of a relatively basal fungus-growing ant, Apterostigma cf. goniodes (Attini), in central Panama. In laboratory colonies, A. cf. goniodes workers attended and cared for the eggs. Two blind snakes, Liotyphlops albirostris (Anomalepididae), successfully hatched, which is the first rearing record for this species. The ants did not disturb the snakes, and the snakes did not eat the ants; we found no ants in the dissected stomachs of the snakes. We review other associations between nesting fungus-growing ants and egg-laying vertebrates, which together suggest that attine nests may provide a safe, environmentally buffered location for oviposition, even in basal attine taxa with relatively small colony sizes.
    Psyche A Journal of Entomology 01/2012; 2012.
  • SUNSHINE A. VAN BAEL, MARC A. SEID, WILLIAM T. WCISLO
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    ABSTRACT: 1. Fungal endophytes are microfungi that reside asymptomatically inside of leaf tissues, increasing in density and diversity through time after leaves flush. Previous studies have suggested that the presence of fungal endophytes in the harvest material of leaf‐cutting ants (Atta colombica, Guérin‐Méneville) may negatively affect the ants and their fungal cultivar.2. In the present study, it was tested whether the presence and diversity of fungal endophytes affected the amount of time necessary for leaf‐cutter ants to cut, process, and plant leaf material in their fungal garden. It was found that ants took 30–43% longer to cut, carry, clean, and plant leaf tissue with high relative to low endophyte abundance, and that the ants responded similarly to leaf tissue with high or low endophyte diversity.3. It was further investigated whether the fungal cultivars' colonisation rate was greater on leaf material without fungal endophytes. No difference in the ants' cultivar colonisation rate on leaf tissue with high or low endophyte abundance was observed.
    Ecological Entomology 01/2012; 37(4). · 1.95 Impact Factor
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    ABSTRACT: Social castes of eusocial insects may have arisen through an evolutionary modification of an ancestral reproductive ground plan, such that some adults emerge from development physiologically primed to specialize on reproduction (queens) and others on maternal care expressed as allo-maternal behaviour (workers). This hypothesis predicts that variation in reproductive physiology should emerge from ontogeny and underlie division of labour. To test these predictions, we identified physiological links to division of labour in a facultatively eusocial sweat bee, Megalopta genalis. Queens are larger, have larger ovaries and have higher vitellogenin titres than workers. We then compared queens and workers with their solitary counterparts-solitary reproductive females and dispersing nest foundresses-to investigate physiological variation as a factor in caste evolution. Within dyads, body size and ovary development were the best predictors of behavioural class. Queens and dispersers are larger, with larger ovaries than their solitary counterparts. Finally, we raised bees in social isolation to investigate the influence of ontogeny on physiological variation. Body size and ovary development among isolated females were highly variable, and linked to differences in vitellogenin titres. As these are key physiological predictors of social caste, our results provide evidence for developmental caste-biasing in a facultatively eusocial bee.
    Proceedings of the Royal Society B: Biological Sciences 11/2011; 279(1732):1437-46. · 5.68 Impact Factor
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    ABSTRACT: Allometric studies of the gross neuroanatomy of adults from nine species of spiders from six web-weaving families (Orbicularia), and nymphs from six of these species, show that very small spiders resemble other small animals in having disproportionately larger central nervous systems (CNSs) relative to body mass when compared with large-bodied forms. Small spiderlings and minute adult spiders have similar relative CNS volumes. The relatively large CNS of a very small spider occupies up to 78% of the cephalothorax volume. The CNSs of very small spiders extend into their coxae, occupying as much as 26% of the profile area of the coxae of an Anapisona simoni spiderling (body mass < 0.005 mg). Such modifications occur both in species with minute adults, and in tiny spiderlings of species with large-bodied adults. In at least one such species, Leucauge mariana, the CNS of the spiderling extends into a prominent ventral bulge of the sternum. Tiny spiders also have reduced neuronal cell body diameters. The adults of nearly all orbicularian spiders weave prey capture webs, as do the spiderlings, beginning with second instar nymphs. Comparable allometric relations occur in adults of both orb-weaving and cleptoparasitic species, indicating that this behavioral difference is not reflected in differences in gross CNS allometry.
    Arthropod structure & development 11/2011; 40(6):521-9. · 1.11 Impact Factor
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    ABSTRACT: Most bees rely on flowering plants and hence are diurnal foragers. From this ancestral state, dim-light foraging in bees requires significant adaptations to a new photic environment. We used DNA sequences to evaluate the phylogenetic history of the most diverse clade of Apoidea that is adapted to dim-light environments (Augochlorini: Megalopta, Megaloptidia and Megommation). The most speciose lineage, Megalopta, is distal to the remaining dim-light genera, and its closest diurnal relative (Xenochlora) is recovered as a lineage that has secondarily reverted to diurnal foraging. Tests for adaptive protein evolution indicate that long-wavelength opsin shows strong evidence of stabilizing selection, with no more than five codons (2%) under positive selection, depending on analytical procedure. In the branch leading to Megalopta, the amino acid of the single positively selected codon is conserved among ancestral Halictidae examined, and is homologous to codons known to influence molecular structure at the chromophore-binding pocket. Theoretically, such mutations can shift photopigment λ(max) sensitivity and enable visual transduction in alternate photic environments. Results are discussed in light of the available evidence on photopigment structure, morphological specialization and biogeographic distributions over geological time.
    Proceedings of the Royal Society B: Biological Sciences 07/2011; 279(1729):794-803. · 5.68 Impact Factor

Publication Stats

1k Citations
308.95 Total Impact Points

Institutions

  • 1994–2014
    • Smithsonian Tropical Research Institute
      Ciudad de Panamá, Panamá, Panama
  • 2011
    • University of California, Los Angeles
      • Department of Ecology and Evolutionary Biology
      Los Angeles, CA, United States
    • Australian National University
      • Division of Biomedical Science and Biochemistry (BSB)
      Canberra, Australian Capital Territory, Australia
  • 2009
    • University of Texas at Austin
      • Department of Integrative Biology
      Texas City, TX, United States
    • Smithsonian Institution
      Washington, Washington, D.C., United States
  • 2004–2008
    • Lund University
      • Department of Biology
      Lund, Skane, Sweden
  • 1987–2008
    • University of Kansas
      Lawrence, Kansas, United States
  • 2003–2007
    • University of Puerto Rico at Rio Piedras
      • Department of Biology
      San Juan, San Juan, Puerto Rico
  • 1999
    • University of Sussex
      Brighton, England, United Kingdom
  • 1992–1996
    • Cornell University
      • Department of Entomology
      Ithaca, NY, United States
  • 1995
    • The University of Arizona
      Tucson, Arizona, United States