Behavioral flexibility in age castes of the antPheidole dentata

Division of labor among size and age classes in social insect colonies is a fundamental aspect of sociality, with such classes typically showing behavioral specialization and being associated with particular tasks for prolonged periods of time (i.e., forming castes). Theoretically, such specialization and division of labor enhance efficiency and, ultimately, reproductive success, and the ratios among members of those castes are hypothesized to be under selection and adaptive. However, our recent field study of the ant Pheidole dentatashowed no correlation between ecological factors which should affect colony growth and those caste ratios but implied flexibility in the association between minor worker age castes and their tasks. In laboratory experiments on behavioral flexibility in minor age castes of P. dentataold workers in colonies without young workers competently perform both old worker (castetypical) and young worker (atypical) tasks, and vice versa. The implications of these results for ergonomie theory are considered.     

Asymmetrical competition and amensalism through soil dumping by the ant, Myrmicaria natalensis

ABSTRACT.

• 1 Myrmicaria natalensis (Smith) (Hym: Formicidae) is a large, predaceous ant that excavates large amounts of soil during nest construction.
• 2 During the winter, 25% of its nests went extinct through resistance and aggression from allospecific ants. The remaining 75% thrived, although one nest was forced to move, but did not go extinct, through intense competition.
• 3 The surviving fifteen M.natalensis nests obliterated forty-one allospecific nests by covering them with excavated soil.
• 4 During spring, M.natalensis nests expanded rapidly and none went extinct, so there was no longer asymmetrical competition but total amensalism in favour of M.natalensis.
• 5 Implications for ant management are that control by trunk banding of honeydew-seeking ants will increase asymmetry towards M.natalensis through positive feedback. This is desirable in that M.natalensis is a highly predaceous ant of pests such as lepidopteran larvae.

     

福建牛肝菌科二新种

报道了闽西北三明市郊和宁化县的牛肝菌科二新种,并简述了该科的四亚科特征。     

Pine sawfly defence and variation in host plant resin acids: a trade-off with growth

Abstract.

• 1 The defence capability of pine sawfly larvae reared on Scots pines with low or high concentrations of resin acids was determined in a field experiment, where larvae were exposed to predatory ants, and in a laboratory experiment in which the rate of defence droplet replenishment was measured.
• 2 Larvae on low resin-acid shoots disappeared faster than larvae on high resin-acid shoots when exposed to predatory ants.
• 3 Larvae fed high resin-acid needles produced 50% larger defence droplets than larvae fed low resin-acid needles.
• 4 In an additional experiment high predation pressure was simulated by repeatedly removing defence droplets. Larvae responded by feeding more on tissue rich in resin acids, but at the cost of a reduction in growth rate.
• 5 Based on these data and earlier findings that survival and development of sawfly larvae are negatively affected by high resin-acid concentrations, we conclude that pine sawflies face a dilemma of conflicting demands, i.e. although high needle resin-acid concentrations enhance defence capability, they also reduce growth and survival. Our data also suggest that it is not necessarily the ovipositing female that has to balance this trade-off: plasticity in larval feeding behaviour provides larvae with a means to at least partly solve the dilemma.

     

Soldier determination in Pheidole bicarinata: Inhibition by adult soldiers

In the ant Pheidole bicarinata, adult soldiers suppress the induction of soldier developments in larvae that have been treated with methoprene, as well as in acetone-treated controls. Induction of soldier development is inhibited in methoprene-treated larvae when the adult soldiers are present as nurses, when they are present in the colony but minor workers serve as nurses, and when they are held in a minor worker-permeable cage to prevent them from contacting larvae. Suppression of soldier determination can be overridden by high doses of methoprene applied during the juvenile hormone-sensitive period for soldier determination. The degree of suppression increases with increasing contact between larvae and adult soldiers. The most likely mechanism of inhibition is a contact soldier pheromone. On the basis of our results, we expand our model of soldier determination to accommodate the fact that the threshold titre of juvenile hormone necessary to induce soldier development changes in the presence of soldiers. A threshold that is sensitive to the presence of adult soldiers provides a mechanism whereby the worker caste ratio in colonies can be regulated.     

Comparative life‐history traits in a fig wasp community: implications for community structure

1. Whether life‐history traits can determine community composition and structure is an important question that has been well explored theoretically, but has received scant empirical attention. Life‐history traits of a seven‐member community of galler and parasitoid fig wasp species (Chalcidoidea), developing within the inflorescences (syconia) of Ficus racemosa (Moraceae) in India, were determined and used to examine community structure and ecology. 2. Gallers were pro‐ovigenic (all eggs are mature upon adult emergence) whereas parasitoids were synovigenic (eggs mature progressively during adult lifespan). Initial egg load was correlated with body size for some species, and there was a trade‐off between egg number and egg size across all species. Although all species completed their development and left the syconium concurrently, they differed in their adult and pre‐adult lifespans. Providing sucrose solutions increased parasitoid lifespan but had no effect on the longevity of some galler species. While feeding regimes and body size affected longevity in most species, an interaction effect between these variables was detected for only one species. 3. Life‐history traits of wasp species exhibited a continuum in relation to their arrival sequence at syconia for oviposition during syconium development, and therefore reflected their ecology. The largest number of eggs, smallest egg sizes, and shortest longevities were characteristic of the earliest‐arriving galling wasps at the smallest, immature syconia; the converse characterised the later‐arriving parasitoids at the larger, already parasitised syconia. Thus life history is an important correlate of community resource partitioning and can be used to understand community structure. 4. This is the first comprehensive study of life‐history traits in a fig wasp community. The comparative approach revealed constraints and flexibility in trait evolution.     

Ant colony optimization as a method for strategic genotype sampling

A simulation study was carried out to develop an alternative method of selecting animals to be genotyped. Simulated pedigrees included 5000 animals, each assigned genotypes for a bi-allelic single nucleotide polymorphism (SNP) based on assumed allelic frequencies of 0.7/0.3 and 0.5/0.5. In addition to simulated pedigrees, two beef cattle pedigrees, one from field data and the other from a research population, were used to test selected methods using simulated genotypes. The proposed method of ant colony optimization (ACO) was evaluated based on the number of alleles correctly assigned to ungenotyped animals (AK_P), the probability of assigning true alleles (AK_G) and the probability of correctly assigning genotypes (APTG). The proposed animal selection method of ant colony optimization was compared to selection using the diagonal elements of the inverse of the relationship matrix (A⁻¹). Comparisons of these two methods showed that ACO yielded an increase in AK_P ranging from 4.98% to 5.16% and an increase in APTG from 1.6% to 1.8% using simulated pedigrees. Gains in field data and research pedigrees were slightly lower. These results suggest that ACO can provide a better genotyping strategy, when compared to A⁻¹, with different pedigree sizes and structures.     

Birds and army ants in a fragment of the Atlantic Forest of Brazil

ABSTRACT Little is known about the birds associated with army‐ant swarms in the Brazilian Atlantic forest. Our objectives were to locate and monitor army‐ant swarms in the Atlantic rainforest of Brazil and to identify the species of birds that attended the swarms and exhibited bivouac‐checking behavior. From July 2004 to August 2005, we located 49 swarms of army ants, including 28 Eciton burchelli, 19 Labidus praedator, and 2 Eciton vagans swarms. No birds were present at 17 (35%) swarms. At 32 swarms where birds were present, 22 (69%) were E. burchelli swarms and 10 (31%) were L. praedator swarms. No birds were observed at the two E. vagans swarms. We identified 66 species of birds attending the swarms, but only 43 species were observed foraging on prey flushed by the ants. Eighteen of these species had not been previously reported to forage in association with army‐ant swarms. Most birds observed during our study attended army‐ant swarms opportunistically, with White‐shouldered Fire‐eyes (Pyriglena leucoptera) the only obligate ant follower. Our observations suggest that the arthropods and other organisms flushed by army ants represent an important food resource for several species of birds in the Atlantic forest ecosystem.     

Myrmica rubra microhabitat selection and putative ecological impact

1. Myrmica rubra (European fire ant) has invaded northern latitude coastal areas in North America. This macroscale distribution suggests that M. rubra is moisture‐ and temperature‐limited, but the distribution of the invaded range may reflect the legacy of original introduction locations preserved by limited dispersal. 2. This study examined a two‐decade population change in M. rubra (1994–2015) and the microscale abiotic (moisture and temperature), biotic (plants), anthropogenic (pesticide) and physiological (thermal tolerance) limits on the invasion at the Tifft Nature Preserve in Buffalo, NY (U.S.A.). Changes in the abundance of native ants and other invertebrates were also examined. 3. Despite localised declines with pesticide treatments, overall M. rubra forager abundance increased 27% between 1994 and 2015. Abundance increased the most in the warmest areas (native ants were unaffected by temperature), but M. rubra colony locations were strongly linked to higher soil moisture and lower soil temperature. Myrmica rubra ants also exhibited relatively low thermal tolerances consistent with high‐latitude and high‐elevation ants. 4. Where local M. rubra populations increased the most, native ant species decreased, and where local M. rubra populations declined, native ant species increased. Some arthropod species had lower abundance with M. rubra presence, but the impacts were less striking. 5. Myrmica rubra population growth was promoted at the microhabitat scale where relatively higher temperatures prompted foraging, and relatively lower temperatures and high moisture supported nesting. These results suggest that macroscale M. rubra invaded‐range distributions in northern climates near coastal areas are replicated at the microscale where the ant prefers cooler, moister microsites.