The First Gynandromorph of the Neotropical Bee Megalopta Amoena (Spinola, 1853) (Halictidae) with Notes on its Circadian Rhythm

Gynandromorphy is an anomaly that results in an organism phenotypically expressing both male and female characteristics. Here we describe the first gynandromorph of the bee species Megalopta amoena (Spinola, 1853) (Halictidae, Augochlorini) and the second record of this anomaly within the genus Megalopta. Additionally, we analyzed the bee’s circadian rhythm, which has never before been quantified for a gynandromorph. The gynandromorph showed a deviant activity pattern; it was intermediate between that of the male and female M. amoena. Our results imply that the brains of bilateral gynandromorphs may have mixed sex-specific signaling. Based on four days of recording, the gynandromorph circadian rhythm was shifted earlier in the day relative to the male and female M. amoena, and it exhibited intensity similar to the female

Developmental plasticity shapes social traits and selection in a facultatively eusocial bee

Developmental plasticity generates phenotypic variation, but how it contributes to evolutionary change is unclear. Phenotypes of individuals in caste-based (eusocial) societies are particularly sensitive to developmental processes, and the evolutionary origins of eusociality may be rooted in developmental plasticity of ancestral forms. We used an integrative genomics approach to evaluate the relationships among developmental plasticity, molecular evolution, and social behavior in a bee species (Megalopta genalis) that expresses flexible sociality, and thus provides a window into the factors that may have been important at the evolutionary origins of eusociality. We find that differences in social behavior are derived from genes that also regulate sex differentiation and metamorphosis. Positive selection on social traits is influenced by the function of these genes in development. We further identify evidence that social polyphenisms may become encoded in the genome via genetic changes in regulatory regions, specifically in transcription factor binding sites. Taken together, our results provide evidence that developmental plasticity provides the substrate for evolutionary novelty and shapes the selective landscape for molecular evolution in a major evolutionary innovation: Eusociality

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

The Effects of In Ovo Cortisol Exposure on Behaviour and Stress Axis Organization in the Threespine Stickleback Gasterosteus aculeatus

Amongst vertebrates, transfer of maternal glucocorticoid (GC) stress hormones to developing embryos through egg yolk (in ovo) or in utero is documented in a variety of species. This phenomenon has attracted attention in recent years because of the significant physiological and behavioural consequences of this early-life GC exposure and their potential relevance to human health and disease progression. Prenatal programming by maternal glucocorticoid exposure has also been proposed to play a role in adaptation, although natural systems in which to test this hypothesis are lacking. In this study, in ovo cortisol treatment of threespine stickleback eggs at physiologically significant levels is used to test the effects of maternal glucocorticoids on juvenile brain expression levels of three candidate stress-axis genes (GR1, GR2, and POMC), and on three stress-linked behaviours thought to be sensitive to maternal GC levels (aggression, boldness, and shoaling). In rats, glucocorticoid receptor (GR) down-regulation leading to reduced glucocorticoid feedback sensitivity and a subsequent increase in stress-axis reactivity is thought to explain decreases in aggression and boldness that often follow maternal GC elevation in that species. I report that, contrary to the bulk of findings in mammalian studies, GR1 and GR2 expression levels in cortisol-treated fish are higher than those seen in untreated fish. Although cortisol treatment influenced gene expression, neither shoaling, aggression nor boldness were strongly influenced by treatment. Sex differences in boldness and aggression levels matched previously described results, which suggests behavioural assaysthat GC-mediated maternal effects on offspring behaviour may not be attributable exclusively to yolk cortisol increases, or perhaps that behavioural changes may have been too subtle to be detected at the dosage used. Ultimately, this study identifies persistent offspring GR up-regulation as a potential consequence of elevated maternal glucocorticoid levels in fish. The diverse roles of GR in physiological and behavioural regulation suggest that the consequences of this up-regulation for survival outcomes are probably complex, a fact that future studies investigating the adaptive significance of glucocorticoid-mediated maternal effects in fish should take care to consider.Science, Faculty ofUnreviewedUndergraduat

The origin of 'queen pheromones': chemical communication as a catalyst for social behavior in the flexibly eusocial bee Megalopta genalis

202 pagesEusociality, a major evolutionary innovation defined by a partitioning of reproduction between genetically related ‘queen’ egg-layers and generally sterile ‘worker’ castes, has arisen numerous times in insects and enables increased ecological dominance. Transitions to eusociality are accompanied by complex signaling systems, frequently involving specific chemicals that mediate coordination of activity at the superorganismal scale. Queen pheromones (QPs) that induce short term behavioral ‘releaser’ and longer term physiological ‘primer’ effects on workers are of critical importance among these various signal axes, because they dictate the defining feature of eusociality: a reproductive differentiation of castes. An overarching aim of this dissertation is to illuminate the early origin of the QP signaling channel, which is ubiquitous among highly eusocial insects but poorly understood in its early stages. Is the early origin of QPs defined by a chemical manipulation of nascent workers against their best interests? Or, alternatively, are primordial QPs honest chemical advertisements of queen reproductive potential, allowing workers to optimally invest in their queens’ reproductive futures? To distinguish between these alternatives, I focus on the tropical sweat bee Megalopta genalis (Hymenoptera: Halictidae), a species representative of the earliest stages of eusocial evolution in which simple eusociality is polyphenic at the population level and workers retain the option of reproducing independently. In chapter 1, I analyze glandular and cuticular chemistry across reproductive (solitaries and queens) and non-reproductive (worker) phenotypes, identifying candidate QPs associated with reproduction and queenship. In chapter 2, I use synthetic mixtures of candidate compounds – linear alkanes, methylalkanes, and macrocyclic lactones in their natural amounts and ratios – to show that a bouquet of methylalkanes (MAs) serves as the QP of M. genalis. I then show that MAs are true signals modulated by social context, which are predictive of queen ovarian development, egg-laying rates, and worker inclusive fitness returns under natural conditions. I also provide evidence that the shared requirement of essential amino acids for queen fecundity (oogenesis) and QP signal (MA) biosynthesis may underpin this predictive relationship. Finally, I find that reproductively labile workers preferentially labor for queens that produce higher amounts of MA, consistent with an ‘honest signal’ role for QPs in enabling optimal allocation of worker reproductive investment. In chapter 3, I close by surveying brood chemistry and demonstrate that MAs occur at a high concentration on the surface of queen-laid eggs. Unlike other eusocial lineages in which QP deposition on eggs occurs, M. genalis is a mass provisioner and workers do not regularly contact the eggs or low-volatility MAs thereon. I argue that MAs on the egg surface have a non-communicative function that may have preceded their evolution as QPs, aligning with a ‘sender-precursor’ model of QP evolution. Taken together, the results of these three chapters are significant in that they demonstrate the use of ‘honest’ QPs prior to the fixation of obligate eusociality, and further indicate that these chemical signals may catalyze the formation of simple eusocial societies. This leads to a view that QPs do not simply arise to meet the communicative needs of advanced eusocial societies, but rather play a more active role in facilitating their evolution by reliably communicating the kin-selected benefits of cooperation

Data from: A split sex ratio in solitary and social nests of a facultatively social bee

Data from: A split sex ratio in solitary and social nests of a facultatively social be

Colony‐level chemical profiles do not provide reliable information about colony size in the honey bee

1. Chemical communication facilitates colony function across social insects, providing workers with information about individual and colony state. Although workers use chemical cues to detect developmental transitions in individuals, it is unknown whether workers can also use colony‐level chemical profiles to detect the developmental state of their colony. Indeed, it is largely unknown how colony‐level chemical profiles change as colonies grow and develop.2. Reproductive onset is a major developmental transition and, in the honey bee, Apis mellifera, colonies must surpass a threshold colony size before workers will invest in reproduction. Given the ubiquity of chemical communication, the present study investigated whether colony‐level chemical profiles change with colony size.3. Chemical compounds deposited by workers of three colony sizes (5000, 10 000, 15 000 workers) collected over a 4‐day time‐series (0, 12, 24, 48, 72, and 96 h), as well as worker cuticular lipids, were sampled.4. In total, 26 compounds deposited on nest surfaces and 20 compounds in worker cuticular lipids were identified; it took up to 24 h for sampled nest surfaces to reach saturation in the number and amount of deposited compounds.5. Among these compounds, no qualitative or quantitative indicators of colony size were found, suggesting that deposited chemical compounds are not semiochemicals in this context. Volatile pheromones have also been shown previously to not play a role in signaling colony size. Therefore, honey bee workers are unlikely to use deposited chemical cues to detect colony size, and must rely instead on other modalities, such as physical cues of worker density.publishe

Cuticular and Glandular Chemistry of Megalopta genalis

These data are from the analysis of cuticular and Dufour’s gland chemistry across alternative social phenotypes within a population of facultatively eusocial Megalopta genalis bees (tribe Augochlorini, family Halictidae). Reproductive bees (queens and solitary reproductives) have distinct glandular and cuticular chemical phenotypes compared with non-reproductive workers. On the cuticle, a likely site of signal transmission, reproductives are enriched for certain alkenes, most linear alkanes, and heavily enriched for all methyl-branched alkanes; these compound classes have known functions as fertility signals among other eusocial insect taxa. Some macrocyclic lactones, compounds that function as queen pheromones in the other eusocial halictid tribe (Halictini), are also enriched among reproductives relative to workers. The intra-population facultative eusociality of M. genalis permits direct comparisons between individuals expressing alternative reproductive phenotypes – females that reproduce alone (solitary reproductives) and social queens – to highlight traits in the latter that are potentially important for eusocial organization. Compared with solitary reproductives, the cuticular chemistries of queens are more strongly differentiated from those of workers and are especially enriched for methyl-branched alkanes. Determining the pheromonal function(s) and information content of the candidate signaling compounds identified will aid in illuminating the early evolutionary history of queen pheromones, chemical signals central to the organization of insect eusociality.This research was supported by fellowships from the Smithsonian Tropical Research Institute, Cornell University, and the Natural Sciences and Engineering Research Council of Canada (to Callum Kingwell)

Data from: A split sex ratio in solitary and social nests of a facultatively social bee

A classic prediction of kin selection theory is that a mixed population of social and solitary nests of haplodiploid insects should exhibit a split sex ratio among offspring: female biased in social nests, male biased in solitary nests. Here we provide the first evidence of a solitary-social split sex ratio, using the sweat bee Megalopta genalis (Halictidae). Data from 2502 offspring collected from naturally occurring nests across six years spanning the range of the M. genalis reproductive season show that despite significant yearly and seasonal variation, the offspring sex ratio of social nests is consistently more female biased than in solitary nests. This suggests that split sex ratios may facilitate the evolutionary origins of cooperation based on reproductive altruism via kin selection