Nestmate discrimination in the queenless ponerine ant Diacamma sp. from Japan

We examined the nestmate discrimination ability of Diacamma sp., an ant that reproduces by colony budding. We also tested for a relationship between internest distance and hostility. Hostility toward non‐nestmates was significantly stronger than that toward nestmates, suggesting that Diacamma sp. discriminates between nestmates and non‐nestmates. There was no significant correlation between internest hostility and internest distance, which indicates the absence of a “dear enemy” phenomenon in this species.     

Shift in the behaviours regulating monogyny is associated with highgenetic differentiation in the queenless ant Diacamma ceylonense

Summary In the queenless ant genus Diacamma, one mated worker (called gamergate) maintains reproductive mono-poly in a colony by mutilating newly emerged workers. However, in several populations from south India, referred to as nilgiri, gamergates do not mutilate their nestmates but monopolize reproduction using dominance interactions . Various lines of evidence indicate that nilgiri populations are closely related to the neighboring species D. ceylonense. To determine whether this important behavioural difference between nilgiri and D. ceylonense is associated with signi-ficant genetic differentiation, we have used microsatellite and mitochondrial markers to examine genetic variation within and between nilgiri and D. ceylonense. We found a very high genetic differentiation between the two forms, which suggests a lack of gene flow. There was an unexpected pattern of mitochondrial variation, because all nilgiri populations show identical or very closely related COII sequences except one population with a very different haplotype. This divergent haplotype is genetically much more distant from the other nilgiri haplotypes than are D. ceylonense haplotypes. This pattern is not observed at the nuclear level, which suggests that introgression of mitochondrial DNA probably occurred in some nilgiri populations.     

Age polyethism,idiosyncrasy and behavioural flexibility in the queenless ponerine ant,Diacamma sp.

Age-related behavioural change of individually marked and known-age workers of a colony ofDiacamma sp. was observed through entire ant lives in the laboratory for more than a year. Although typical age polyethism was observed, activity of inside and outside tasks, life span, or time schedule of behavioural change varied considerably among workers. Idiosyncrasies in age-related behavioural change was detected among workers that eclosed on the same day. Cluster analyses revealed that individual patterns of behavioural change tended to be different when eclosion dates were far apart. This suggests that most workers change their behaviour flexibly. Thus, there is little effect of idiosyncrasy on colony response to changes in colony condition.     

Differentiation of the reproductive tract between dominant and subordinate workers in the Japanese queenless ant Diacamma sp.

In queenless ants, gamergates (mated egg‐laying workers) fulfil the reproductive task normally reserved for the queen. Every worker is a potential gamergate, thus we expect pronounced conflicts over sexual reproduction within their colonies. In the queenless ant genus Diacamma, gamergates inhibit nest mates from mating by aggressively removing (‘mutilating’) a pair of small appendages on the thorax, termed gemmae, shortly after eclosion. Dissection and serial sectioning of the reproductive tracts of both mutilated and unmutilated individuals of Diacamma sp. from Japan at different ages revealed that mutilation inhibits the development of the bursa copulatrix and the spermatheca, two structures fundamental for sexual reproduction. The precursor of the bursa copulatrix develops into a fully functional structure in unmutilated individuals, whereas it degenerates irreversibly in mutilated callows. Experimental manipulations showed that the removal of the gemmae is not the sole factor regulating this development. The spermathecal epithelium and accessory spermathecal gland of unmutilated individuals are thicker than that of mutilated individuals, indicating a higher degree of activity in the former. Mutilated females are therefore left incapable of copulating and less competent for long‐time sperm storage.     

Population genetic structure and male-biased dispersal in the queenless ant Diacamma cyaneiventre

In this study we investigated the population genetic structure of the queenless ant Diacamma cyaneiventre. This species, lacking winged queens, is likely to have a restricted female dispersal. We used both mitochondrial and microsatellite markers to assess the consequence of such restricted female dispersal at three geographical scales: within a given locality (< 1 km), between localities within a given region (< 10 km) and between regions (> 36 km). Within a locality, a strong population structure was observed for mitochondrial DNA (mtDNA) whereas weak or nonexistent population genetic structure was observed for the microsatellites (around 5% of the value for mtDNA). Male gene flow was estimated to be about 20-30 times higher than female gene flow at this scale. At a larger spatial scale, very strong genetic differentiation for both markers was observed between localities - even within a single region. Female dispersal is nonexistent at these scales and male dispersal is very restricted, especially between regions. The phylogeographical structure of the mtDNA haplotypes as well as the very low genetic diversity of mtDNA within localities indicate that new sites are colonized by a single migration event from adjacent localities, followed by successive colony fissions. These patterns of genetic variability and differentiation agree with what is theoretically expected when colonization events are kin-structured and when, following colonization, dispersion is mainly performed by males.     

Decreased immune response as a proximate cost of copulation and oviposition in a damselfly

Abstract.Males and females of the Japanese calopterygid damselfly, Matrona basilaris japonica Fester, showed a rapid (within 24 h), and significant reduction in immune system function (encapsulation response) after reproductive activity (copulation or oviposition).
 A similar, but non‐significant, change occurred in males that conducted energetically costly behaviour (fighting).
 These data suggest that there may be physiological costs other than energy‐based trade‐offs associated with copulation and oviposition that may have life‐history consequences via their effects on immune system function.     

The energetic cost of reproductive conflicts in the ant Pachycondyla obscuricornis

In a variety of social animals, individuals can secure reproductive rights through aggressive dominance. Direct individual benefits of aggression are widely recognized, but underlying costs affecting group productivity, and thus indirect benefits, are less clear. Costs of aggressive regulation of reproduction are especially important in small social insect colonies, where individual workers could potentially dominate male production. We estimated the energetic costs associated with the regulation of worker reproduction in the ponerine ant Pachycondyla obscuricornis, using the total CO2 emission of a colony as a measure. The level of CO2 emission of 12 experimental colonies varied significantly during five periods with varying levels of aggression and egg-laying. Overall, CO2 emission increased with the degree of fighting in a colony, but was not associated with differences in egg-laying. Aggressive regulation of reproduction and the formation of a dominance hierarchy thus pose an energetic cost to the colony. Furthermore, workers reduce their work-activities immediately after experimental orphaning, giving a further cost to the colony. These costs might influence the outcome of conflicts over male production in ants. This paper presents the first quantification of energetic costs of aggressive behavior regulating reproduction in ants.     

Reproductive conflict among ant workers inDiacamma sp. from Japan: dominance and oviposition in the absence of the gamergate

Summary Queens do not exist inDiacamma sp. from Japan, and a single worker (gamergate) mates and monopolizes reproduction in each colony. We isolated small groups of workers without the gamergate, and confirmed that after 7–15 days many workers were able to oviposit (Tab. 1). These egg-laying individuals engage in stereotyped attacks towards each other. In six groups of individually marked workers (Tabs. 3 to 7), the pattern of aggressive interactions always indicated that one worker was dominant. She usually initiated a large number of attacks, but was herself never attacked. This dominant worker (alpha) also ate the eggs just laid by others. There was no linear dominance hierarchy, although a second highest-ranking worker could be recognized (she was only attacked by alpha). When these workers were dissected 4–6 weeks after being orphaned, only the alpha worker had active ovaries; other individuals that had been observed to oviposit earlier exhibited resorbed ovaries. Dissection of another 12 orphaned groups, kept together for different periods of time (Tab. 2), confirmed that one dominant worker is able to suppress the ovarian activity of all others in her group. We discuss how these aggressive interactions also function to regulate the production of males in other contexts, even when the gamergate is present. This aggression is separate, however, from another competitive interaction, mutilation of the gemmae, that functions as a control of mating activity in this species.     

Ovarian development and insulin-signaling pathways during reproductive differentiation in the queenless ponerine ant Diacamma sp.

In many social hymenopteran species, workers possess functional ovaries that are physiologically inactive in the presence of queens. We investigated the ovarian regulatory mechanism of workers and reproductives in a queenless ponerine ant, Diacamma sp., using histological and molecular techniques. In this ant, clear reproductive differentiation occurs via a highly sophisticated dominance behavioral interaction called “gemmae mutilation”. This clear and rapid bifurcation of reproductive physiology allows us to elucidate the detailed ovarian differentiation process. Histological characteristics of functional ovaries (fusomes and ring canals) were found in both workers and reproductives, suggesting that early oogenesis is not blocked in workers. Since insulin/insulin-like growth factor signaling (IIS) is known to control insect reproduction, orthologs of 2 positive IIS regulators, insulin receptor and serine-threonine kinase Akt (protein kinase B), were cloned in Diacamma (DiaInR, DiaAkt); their expression patterns during reproductive differentiation were examined by real-time quantitative polymerase chain reaction; DiaInR and DiaAkt were strongly expressed in the gasters of reproductives. Whole-mount in situ hybridization of ovaries indicated that DiaInR and DiaAkt were expressed in nurse cells, oocytes, and upper germarial regions of reproductives but not of workers. Our data suggest that the IIS pathway accounts for reproductive differentiation in late oogenesis.     

Reproductive development and ontogeny of queen pheromone production in the fire ant Solenopsis invicta

Queens of the fire ant, Solenopsis invicta Buren, produce several releaser and primer pheromones. Using bioassays, the ontogeny of three of these pheromones related to reproductive development was investigated. Virgin queens, in which the process of wing-shedding (dealation) serves as an indicator of the initiation of reproductive development, were studied. First, the production of two queen pheromones produced in the poison gland was examined. The pheromone responsible for initiation and maintenance of retinue formation, a releaser effect, was found to be produced in detectable quantities 2 days after dealation, at which time queens showed significant ovary development and many (30%) had started laying eggs. A primer pheromone that inhibits alate virgin queens from dealating was detected in queens 3 days following wing-shedding, when 80% of the queens were ovipositing. Second, I examined the onset of a pheromone of unknown glandular origin produced by reproductively active virgin queens which leads to their destruction in queenright colonies by stimulating workers to attack and kill them. This pheromone is secreted in quantities detectable by bioassay 2 days after dealation. Thus, in S. invicta, the ontogeny of three distinct queen pheromones is tightly linked with ovary development and initiation of egg laying. These results demonstrate reproductive and communicative functions are closely associated during the transition from potential to functional queen.     

A genetic correlation between age at pupation and melanization immune response of the yellow fever mosquito Aedes aegypti

To investigate the evolutionary cost of an immune response, we selected six lines of the mosquito Aedes aegypti for earlier or later pupation and measured the extent to which this selection procedure changed the mosquito's ability to encapsulate and melanize a negatively charged Sephadex bead. After 10 generations of selection, the age at pupation in the two selection regimes differed by about 0.7 days, accompanied by an increase of wing length of the mosquitoes selected for late pupation. Among the mosquitoes that had been selected for early pupation, only 6% had strongly or completely melanized the bead, while among the individuals that had been selected for late pupation, 32% had melanized the bead. Thus, our results suggest a genetic correlation between age at pupation and immunocompetence. As a consequence, mosquitoes that respond to increased intense parasite pressure with more effective immunity are predicted to pay for the increased defense with slower development.     

Reproductive success and the energetic cost of parental care in male smallmouth bass

Direct field measurements of the energetic expenditure on parental care and within-nest reproductive success of individual male smallmouth bass Micropterus dolomieui were determined by measuring the change in total body mass as well as by total body electroconductivity analysis (TOBEC™). With TOBEC, the change in total body lean mass of the same live individual was measured non-destructively at the beginning and end of the parental care period. Lean mass was the primary source of energy utilized during parental care indicating starvation and potential loss of future reproduction. Individual loss in lean mass was related positively to reproductive success suggesting that the energy expended during parental care does affect individual fitness.     

Reproductive effort and floral photosynthesis in Spiranthes cernua (Orchidaceae)

This study examined the cost of reproduction and photosynthetic characteristics of the reproductive structures of Spiranthes cernua, an agamospermic, terrestrial orchid. Reproduction was frequent: two-thirds of the plants flowered at least 2 yr in a row and one-fourth of the consecutive-year runs were ~3 yr. Neither a significant decrease in leaf area nor a reduced likelihood of flowering was observed following 1 or 2 yr of inflorescence production. While there was a tendency for plants producing >16 flowers to have decreased size the next year, plants with the greatest number of flowers (31+) were the most likely to reproduce. Leaf and reproductive gas exchange were measured in the field. Low but positive rates of net photosynthesis were documented at all stages of inflorescence development. The average rates of photosynthesis for each stage were: leaves, 9.2 mmol CO2/m2s; inflorescence in bud, 3.7 mmol CO2/m2s; inflorescence in flower, 2.5 mmol CO2/m2s and infructescence, 0.2 mmol CO2/m2s. Based on diurnal gas exchange, the contribution of leaves and reproductive structures to seasonal carbon assimilation was 91.6 and 8.4%, respectively. The role of the inflorescence as a source and sink for carbon assimilation may lower the cost of reproduction and support frequent inflorescence production.     

Amino acid sources in the adult diet do not affect life span and fecundity in the fruit-feeding butterfly Bicyclus anynana

Abstract.  1. In tropical forests, the adults of many butterfly species feed on fruits rather than nectar from flowers and have long life spans. Rotting fruit and nectar differ from each other in many respects, including sources of amino acids and microbial life. If amino acids in the adult diet can be used for reproduction, this may have facilitated the evolution of extended life spans in this guild.
2. This issue was addressed by investigating effects of banana, yeast, and amino acids in the adult diet of the fruit-feeding butterfly Bicyclus anynana (Lepidoptera) on longevity and female reproductive output in two experiments.
3. Results showed that in the fruit-feeding butterfly B. anynana : (i) banana juice, but not sliced banana or added amino acids extend life span compared with a sugar solution of similar composition; (ii) compared with this sugar solution, other cohorts (banana juice-amino acid enriched) did not have significantly higher reproductive outputs; (iii) yeast does not represent a valuable source of nutrients; (iv) caloric restriction may cause decreased life span and rate of reproduction; and (v) increased rates of reproduction have a life span cost.     

Reproductive allocation and the long-term costs of reproduction in Siparuna grandiflora, a dioecious neo-tropical shrub

1 Using a combination of observational and experimental approaches, both allocation of resources to reproduction (often called the direct cost of reproduction) and the subsequent long-term costs (the indirect, delayed or demographic cost) associated with reproductive allocation to male and female function in Siparuna grandiflora (Siparunaceae), a tropical dioecious shrub, were examined.
2 The objectives were to determine whether females allocate more biomass or nitrogen per reproductive episode than males, and whether there is a long-term cost of reproduction in terms of subsequent growth or reproduction for either sex. If there is no long-term cost of reproduction, then reproduction may be viewed as free in an evolutionary sense.
3 As is generally the case in dioecious species, females allocated more biomass and nitrogen to reproduction than males. Females also showed delayed costs of reproduction in terms of decreased growth and subsequent reproduction, whereas males did not.
4 The lack of measurable delayed costs in males suggests that with the evolution of dioecy, selection has reduced delayed costs of reproduction in S. grandiflora males. In contrast, females that were prevented from reproducing were able to re-allocate resources to growth, and produced more stem length on average than males. This re-allocation response may have evolved to reduce delayed costs of reproduction in females over time frames longer than that considered in the present study.