Colony Reproductive Output Research Articles

Studies on the novel effects of electron beam treated pollen on colony reproductive output in commercially-reared bumblebees (Bombus terrestris) for mass pollination applications

Commercially-reared bumblebees provide an important pollinator service that helps support food production and security. The deployment of an appropriate non-thermal disinfection technology for the bulk treatment of pollen collected from honeybees for the feeding of commercial bumblebees is important in order to mitigate against complex diseases and unwanted pathogen spillover to native bees. High level disinfection of pollen was achieved using an electron (e)-beam dose of 100 kGy that corresponded to 78 % loss of cellular viability of bee pathogens before feeding to bumblebees as measured by the novel in vitro use of flow cytometry (FCM). Novel findings showed that e-beam treated-pollen that was fed to bumblebees produced fewer females, gynes and exhibited an absence of males when compared to control bumblebee colonies that were fed untreated commercial pollen. A similar trend emerged in bumblebee colony reproductive outputs when using membrane filtered washed pollen. Proteomic analysis of bumblebees from individual colonies fed with treated-pollen revealed a differential abundance of proteins associated with stress, immunity and metabolism when compared to the untreated pollen control group. Microbiome analysis of the bumblebee gut content revealed differences in microbiota between treated and untreated pollen in bumblebee colony studies. This novel study evaluated the impact of industrial e-beam treated-pollen on complex bee disease mitigation where physically treated-pollen fed to bumblebees was shown to substantially affect colony reproductive outputs.

Consistent Monthly Reproduction and Completion of a Brooding Coral Life Cycle through Ex Situ Culture

The continuing impact of local and global stressors on coral reefs worldwide is prompting the exploration of novel approaches aimed at mitigating and improving the bleak future projections for corals. Ex situ aquaculture has the potential to provide a standardized supply of source corals to support active intervention-based research endeavours as well as complementary reef restoration initiatives. To effectively achieve this supply of coral, however, ex situ aquaculture systems need to be able to efficiently maintain reproducing colonies, and have the capacity to support each coral life stage. We monitored the monthly reproduction of the brooding coral, Pocillopora acuta, for one year in two distinct aquaculture systems: a natural seawater-supplied flow-through system (FTS) and an artificial seawater-supplied recirculating aquaculture system (RAS). The coral colonies in both aquaculture systems showed relatively consistent reproduction over time (on average > 70% of all colonies reproducing each month) and maintained natural diel reproduction patterns even after 1 year of ex situ culture. Coral colony reproductive output and timing (i.e., lunar day of release) differed between aquaculture systems in some, but not all, seasons. Planulae released from colonies settled and grew to reproductive size after ~16 months of culture, resulting in the ex situ production of an F2 generation of a brooding coral within two distinct aquaculture systems. This demonstrated that the use of ex situ aquaculture could be directly applied to research, restoration, and conservation aimed at mitigating coral decline in a future marred by climate change and local impacts.

Contrasting effects of land cover on nesting habitat use and reproductive output for bumble bees

AbstractUnderstanding habitat quality is central to understanding the distributions of species on the landscape, as well as to conserving and restoring at‐risk species. Although it is well known that many species require different resources throughout their life cycles, pollinator conservation efforts focus almost exclusively on forage resources. In this study, we evaluate nesting habitat for bumble bees by locating nests directly on the landscape. We compared colony density and colony reproductive output for Bombus impatiens, the common eastern bumble bee, across three different land cover types (hay fields, meadows, and forests). We also assessed nesting habitat associations for all Bombus nests located during surveys to tease apart species‐specific patterns of habitat use. We found that B. impatiens nested under the ground in two natural land cover types, forests, and meadows, but found no B. impatiens nests in hay fields. Though B. impatiens nested at similar densities in both meadows and forests, colonies in forests had much higher reproductive output. In contrast, B. griseocollis tended to nest on the surface of the ground and was almost always found in meadows. B. perplexis was the only species to nest in all three habitat types, including hay fields. For some bumble bee species in this system, meadows, the habitat type with abundant forage resources, may be sufficient to maintain them throughout their life cycles. However, B. impatiens might benefit from heterogeneous landscapes with forests and meadows. Results for B. impatiens emphasize the longstanding notion that habitat use is not always positively correlated with habitat quality (as measured by reproductive output). Our results also show that habitat selection by bumble bees at one spatial scale may be influenced by resources at other scales. Finally, we demonstrate the feasibility of direct nest searches for understanding bumble bee distribution and ecology.

Individual and combined impacts of sulfoxaflor and Nosema bombi on bumblebee (Bombus terrestris) larval growth.

Sulfoxaflor is a globally important novel insecticide that can have negative impacts on the reproductive output of bumblebee (Bombus terrestris) colonies. However, it remains unclear as to which life-history stage is critically affected by exposure. One hypothesis is that sulfoxaflor exposure early in the colony's life cycle can impair larval development, reducing the number of workers produced and ultimately lowering colony reproductive output. Here we assess the influence of sulfoxaflor exposure on bumblebee larval mortality and growth both when tested in insolation and when in combination with the common fungal parasite Nosema bombi, following a pre-registered design. We found no significant impact of sulfoxaflor (5 ppb) or N. bombi exposure (50 000 spores) on larval mortality when tested in isolation but found an additive, negative effect when larvae received both stressors in combination. Individually, sulfoxaflor and N. bombi exposure each impaired larval growth, although the impact of combined exposure fell significantly short of the predicted sum of the individual effects (i.e. they interacted antagonistically). Ultimately, our results suggest that colony-level consequences of sulfoxaflor exposure for bumblebees may be mediated through direct effects on larvae. As sulfoxaflor is licensed for use globally, our findings highlight the need to understand how novel insecticides impact non-target insects at various stages of their development.

Lower bumblebee colony reproductive success in agricultural compared with urban environments.

Urbanization represents a rapidly growing driver of land-use change. While it is clear that urbanization impacts species abundance and diversity, direct effects of urban land use on animal reproductive success are rarely documented. Here, we show that urban land use is linked to long-term colony reproductive output in a key pollinator. We reared colonies from wild-caught bumblebee (Bombus terrestris) queens, placed them at sites characterized by varying degrees of urbanization from inner city to rural farmland and monitored the production of sexual offspring across the entire colony cycle. Our land-use cluster analysis identified three site categories, and this categorization was a strong predictor of colony performance. Crucially, colonies in the two clusters characterized by urban development produced more sexual offspring than those in the cluster dominated by agricultural land. These colonies also reached higher peak size, had more food stores, encountered fewer parasite invasions and survived for longer. Our results show a link between urbanization and bumblebee colony reproductive success, supporting the theory that urban areas provide a refuge for pollinator populations in an otherwise barren agricultural landscape.

Drone “quality” and caste interactions in the honey bee, Apis mellifera L.

We investigated the influence of drone size and potential reproductive quality on caste interactions by adding large drones reared in drone cells (DC drones; considered to be of higher quality) and small drones reared in worker cells (WC drones; of lower quality) to two observation colonies and monitoring worker–drone interactions and acceptance by workers. When initially introduced into the colonies more DC drones received trophallaxis, whereas more WC drones received aggression and eviction attempts from workers. Nevertheless, WC and DC drones were equally likely to be accepted by workers. For both drone types accepted individuals had slightly, but significantly greater weights than rejected males. Thus, workers discriminated between drones of different sizes and potential quality upon initial encounter, although these discriminations were not strongly associated with acceptance decisions. After drones were accepted, workers either showed no preference for interacting with WC or DC drones, or if a preference was shown it tended to favor WC drones. Compared to accepted DC drones, significantly more WC drones received grooming for longer periods of time and also spent more time engaged in all interactions with workers combined. DC and WC drones did not differ in the likelihood of receiving trophallaxis or the vibration signal, although for both interactions slightly more WC drones were recipients. Thus, workers may bias some interactions with accepted drones to favor smaller individuals with potential developmental deficiencies, in a manner that could contribute to the production of a greater total number of competitive males and increased colony reproductive output.

The influence of drone physical condition on the likelihood of receiving vibration signals from worker honey bees, Apis mellifera

Honey bee workers will perform vibration sig- nals on adult drones, which respond by increasing the time spent receiving trophallaxis. Because trophallaxis provides the proteins for sexual maturation, workers could direct vibration signals towards drones showing certain physical characteristics, potentially influencing drone development and colony reproductive output. We examined the influence of drone condition on the likelihood of receiving vibration signals by comparing body weight, protein concentrations, and hemolymph juvenile hormone (JH) titers between drones that received the vibration signal and same-age, non- vibrated controls. Vibrated and control drones did not differ in total body weight, abdomen weight, abdomen-to-body weight ratio, total protein concentrations, or hemolymph JH titers. In contrast, vibrated drones had significantly lower thorax weight and smaller thorax-to-body weight ratios compared with controls. Because relative thorax weight may affect flight ability and mating success, workers could use the vibration signal to increase the care received by less developed drones, potentially contributing to the production of greater numbers of competitive males. However, the differences in thorax weights, while significant, were very small, and it is unknown how such slight differences might be assessed by workers or affect drone performance. Nev- ertheless, vibration signals performed on drones may pro- vide opportunities for exploring the effect of the quality of reproductive individuals on caste interactions in honey bees.

Parentage Outcomes in Response to Estrogen Exposure are Modified by Social Grouping in Zebrafish

Evidence has recently emerged that endocrine-disrupting chemicals (EDCs) can affect various behaviors, including dominance and aggression in social groups, including fish. This study investigated the effect of short-term exposure of male adult zebrafish to 17alpha-ethinylestradiol (EE(2)) on subsequent reproductive output and parentage in colonies with differing numbers of competing males. It was predicted that impacts of EDCs might differ in social groups of fish of differing size because of the greater costs of maintaining dominance hierarchies in large groups. Adult male zebrafish were exposed for 14 days to clean water, 2 ng/L EE(2) or 10 ng/L via the water, prior to placement into colonies in clean water with unexposed females. Exposure to EE(2) at the concentrations adopted prior to the breeding trials did not significantly affect subsequent colony reproductive output. The reproductive success of the most reproductively successful (MRS) male within colonies containing two males (relative to controls) was also unaffected. There was, however, a significant impact of previous EE(2) exposure in tanks containing four males, resulting in a reduction in paternity for the most successful male. Hence, nonlethal behavioral impacts of even short-term exposure to EDCs can have significant impacts on social dominance hierarchies and population genetic diversity.

Colony defense and behavioral differentiation in the eusocial shrimp Synalpheus regalis

The sponge-dwelling shrimp Synalpheusregalis and several congeners exhibit monogynous, eusocial colony structures, and field data suggest that these social species may have a competitive advantage in crowded environments. We explored mechanisms of colony defense, a likely contributor to such a social advantage, by measuring responses of resident shrimp to conspecific and heterospecific intruders in experimental nests. To test for behavioral differentiation among classes of individuals, we compared responses of juvenile, large male, and breeding female (queen) S. regalis to each intruder type. Colony residents discriminated nestmates from both foreign conspecific and heterospecific intruders, making more aggressive snaps and fewer contacts with such intruders than with controls from the same colony. S. regalis colonies also exhibited behavioral differentiation among classes of individuals: most snaps against intruders were by large males. Thus, large males defended the colony, allowing juveniles and the queen to feed and grow unmolested. On a per-individual basis, intruders more frequently contacted the queen than either large males or juveniles, possibly indicating that signals from the queen provide information about colony status as they do in many social insects. Sampling of unmanipulated field colonies showed that colony reproductive output increased linearly, by a factor of 177 times, throughout the range in sampled colony sizes (2–356 individuals), whereas average per capita reproductive output decreased by only 61% over the same range. These data suggest that non-breeding colony members may gain inclusive fitness benefits by remaining in and helping defend the natal sponge. Differentiation among individuals in reproductive and defensive behavior may enhance the efficiency and productivity of S. regalis colonies and contribute to their apparent competitive advantage over less social congeners.

Size-dependent reproduction in the Caribbean gorgonian Pseudoplexaura porosa

Reproductive success among clonal taxa is often portrayed as a simple function of clone size, but reproduction in Pseudoplexaura porosa (Houtuyn), a common Caribbean gorgonian, reflects a more complex relationship between size and gamete production. Tagged colonies were sampled at two reefs in the San Blas Islands, Panama during the 1995 spawning season to determine the colony size at first reproduction, size-dependent polyp fecundities, and whole colony gonad production, and to follow the gametogenic cycle. Additional data were obtained during non-spawning months in 1984 and 1985. Of 120 colonies ranging in height from 20 to 250 cm, only colonies taller than 50 cm were reproductive. An average of 4.33 oocytes polyp−1, 560 to 800 μm in diameter, were released during monthly synchronous spawning events from June to September. Oocytes released each month developed from a group of intermediate size oocytes present at the end of the preceding month. Almost all oocytes >560 μm were released during each spawning event. Spermatogenesis was a shorter process than oogenesis. During each spawning month, mature spermaries developed from a group of 190 μm were released each month, and most of the spermary volume in mature male polyps was generated anew each month of spawning. Among reproductive colonies, polyp fecundity increased with colony height from 50 to 200 cm. Per capita fecundity of >200 cm tall female colonies was lower than for 150 to 200 cm colonies, but whole colony fecundity of large colonies was greater due to the exponential increase in the number of polyps that occurs with increasing colony height. In male colonies, both polyp and colony reproductive output increased with colony height. The large amounts of sperm produced by large male colonies probably contributes to the high rates of in situ fertilization observed in P. porosa. Differences in fecundity as a function of colony size and sex suggest differences in some combination of the cost of reproduction and/or allocation of resources to reproduction.

FOOD FROM SEED-DISPERSAL MUTUALISM SHIFTS SEX RATIOS IN COLONIES OF THE ANTAPHAENOGASTER RUDIS

Workers of Aphaenogaster rudis collect seeds of many species of spring-flowering, perennial herbs. This is part of a seed-dispersal system (myrmecochory) for which benefits to plants are documented, but consequences to ants have not been quantified. To test the predictions that colony size or reproductive output will be enhanced as a consequence of ants collecting seeds, we conducted a field experiment in a forest near Gambier, Ohio, in June and July 1993. Experimental colonies receiving seeds of Sanguinaria canadensis (N = 24 colonies) had ∼3.5 times as many gynes as control colonies (N = 27). Only 25% of control colonies produced any gynes, whereas 65% of experimental colonies did so. Control colonies produced as many males as experimental colonies. Access to seeds shifted the mass and numerical investment ratio in colony reproductive output toward female bias but did not affect the number of workers or queen size. These data support the hypothesis that myrmecochory is a true mutualism. Additionally, the experiment indicates that resource levels influence investment ratios in reproductive ants.

Growth Rates and Growth Strategy in a Clonal Marine Invertebrate, the Caribbean Octocoral Briareum asbestinum.

Colony form directly effects colony reproductive output among colonial benthic invertebrates. The relationship between reproductive effort, colony form, and growth rate in colonies of the Caribbean octocoral Briareum asbestinum were examined by measuring the growth rates of 118 tagged colonies on Pinnacles and House Reef in the San Blas Islands, Panama. Colony growth rates, individual branch growth rates, and branch addition rates were measured over six month intervals from July 1986 to July 1988. Colonies grew at a net rate of 16.6 cm/year and added 1.2 branches/year. Individual branch measurements yielded a net rate of growth of 2.02 cm/year/branch. Positive growth rates, which provide a measure of minimum potential growth, were 71.3 cm/year, and 8.7 branches/year for colonies and 6.21 cm/year for individual branches. Net growth rates and branch addition rates were 76 and 85% less than potential growth rates indicating large losses to fragmentation and predation. Calculated mean longevity of individual colonies (ramets) is short (10.6 years), given observed rates of growth and loss. However, since fragmented branches can reattach and initiate new colonies, losses due to fragmentation contribute to the asexual expansion of the genet. In July 1987, 783 branches on the tagged colonies were individually mapped in order to characterize the relationship between branch size and the number of bifurcations (tips), and growth rates. The best predictor of growth rate was the number of tips per branch (r2 = 0.46; P < .0001). No relationship was found between branch growth and branch size, consequently branch growth per unit length decreased as branch size increased. The independence of branch growth and size may reflect the diversion of energy away from growth toward reproduction. As a consequence of this pattern, bifurcating growth forms will, on a colony basis, grow more rapidly and amass more reproductive tissue than simple linear extension. However, the short longevity of ramets of Briareum asbestinum limits the advantage to be gained from accumulating reproductive tissue by rapid branch bifurcation.

The evolution of queen‐rearing nepotism in social Hymenoptera: Effects of discrimination costs in swarming species

AbstractPolyandry by social hymenopteran queens leads to a potential worker reproductive strategy of rearing full‐sister queens in preference to half‐sister queens. If there is no cost to discrimination, discriminatory queen rearing will be the ESS. However, if discrimination has a cost this conclusion is weakened. This study examines the effect of a “worker efficiency cost” (i.e. discriminatory, nepotistic workers are less effective than non‐nepotistic workers in working to increase total colony reproductive output) on the invasion of rare “nepotist” and “non‐nepotist” alleles in a population in which the other allele is near fixation. Efficiency costs are considered of special relevance to species with swarm founded colonies (e.g., army ants, honey bees).Two analyses are presented: 1) A general model exploring the effects of efficiency costs, the queen‐rearing‐biasing ability of nepotists, and queen mating frequency on invasion of nepotists and non‐nepotists; 2) a discriminatory removal model, in which the actual amount of biasing is dependent on recognition abilities and the discriminatory intensity of nepotists, queen mating frequency, and whether or not removed immature queens are replaced.The results of the removal model indicate that when queen mating frequency is close to one (i.e., because of double mating with unequal sperm use or mixed double and single mating) non‐nepotist is likely to be the ESS. At a higher mating frequency nepotist will become the ESS. At even higher mating frequencies, non‐nepotist may reinvade. This latter conclusion is robust across all models. In particular, non‐nepotists may reinvade at the high mating frequencies found in the honey bee (10–20) if their work efficiency is only a few percent higher than nepotists (the exact amount depends on recognition errors and the intensity of discrimination), resulting in a genetic polymorphism of both nepotists and non‐nepotists. Results of a recent study of patriline discrimination in honey bees (Page et al., 1989) are consistent with such a polymorphism.

The social behavior of Leptothorax allardycei (Hymenoptera, Formicidae): time budgets and the evolution of worker reproduction

Summary. The use of time by workers of the ant Leptothorax allardycei (Mann) is examined. Theoretical predictions are developed concerning the maximal lowering in colony reproductive output that is consistent with the evolution of worker production. Measurements are made of the effect of aggression on colony efficiency. Analysis of time budgets indicate that a typical ant spends a large fraction (0.55) of its time quiescent and another large fraction of time (0.32) involved in undifferentiated activity. Dominance activity and brood care together make up about 11% of the total time. The amount of time spent on dominance activity is negatively related to the amount of time spent on brood care, but positively related to the amount of time that an ant is active. The amount of time that an ant has available for brood care which is actually spent on brood care declines with the amount of time spent on dominance activity. The amount of time that a worker spends feeding liquid food to larvae is a function of hierarchy rank; alpha spends the most time, beta less and gamma still less. The spread of the trait of worker reproduction is examined theoretically, with particular regard to the associated costs to colony reproduction. Worker reproduction can spread through a population, under a variety of formulations, provided the cost to colony reproduction is less than some critical value in the neighborhood of 0.17-0.22 of the total colony output. The cost of worker reproduction in L. allardycei is estimated in two ways: as a time cost and as a reduction in the total number of brood tended per unit time. The two estimates of cost are 0.15 and 0.13 respectively. The reproductive options of the worker caste and the division of reproductive labor vary considerably between species. Reproduction by workers yields fitness differences between workers and results in competition among workers with the result that colony efficiency is affected.