A life history continuum in the males of a Neotropical ant assemblage: refuting the sperm vessel hypothesis

Animal lifespans range from a few days to many decades, and this life history diversity is especially pronounced in ants. Queens can live for decades. Males, in contrast, are often assumed to act as ephemeral sperm delivery vessels that die after a brief mating flight—a view developed from studies of lekking species in temperate habitats. In a tropical ant assemblage, we found that males can live days to months outside the nest, a trait hypothesized to be associated with female calling, another common mating system. We combined feeding experiments with respirometry to show that lifespan can be enhanced over 3 months by feeding outside the nest. In one focal female calling species, Ectatomma ruidum, feeding enhanced male lifespan, but not sperm content. Extended lifespans outside the nest suggest stronger than expected selection on premating traits of male ants, although the ways these traits shape male mating success remain poorly understood.     

Dynamics of sperm transfer in the ant Leptothorax gredleri

Mating tactics differ remarkably between and within species of social Hymenoptera (bees, wasps, ants) concerning, e.g., mating frequencies, sperm competition, and the degree of male sperm limitation. Although social Hymenoptera might, therefore, potentially be ideal model systems for testing sexual selection theory, the dynamics of mating and sperm transfer have rarely been studied in species other than social bees, and basic information needed to draw conclusions about possible sperm competition and female choice is lacking. We investigated sperm transfer in the ant Leptothorax gredleri, a species in which female sexuals attract males by “female calling.” The analysis of 38 female sexuals fixed immediately or up to 7 days after copulation with a single male each revealed that the sperm is transferred into the female bursa copulatrix embedded in a gelatinous mass, presumably a spermatophore. Sperm cells rapidly start to migrate from the tip of the spermatophore towards the spermatheca, but transfer is drastically slowed down by an extreme constriction of the spermathecal duct, through which sperm cells have to pass virtually one by one. This results in the spermatheca being filled only between one and several hours after mating. During this time, the posterior part of the spermatophore seals the junction between bursa copulatrix and spermathecal duct and prevents sperm loss. The prolonged duration of sperm transfer might allow female sexuals to chose between ejaculates and explain previously reported patterns of single paternity of the offspring of multiply mated queens. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Imperfect chemical female mimicry in males of the ant Cardiocondyla obscurior

Winged and wingless males coexist in the ant Cardiocondyla obscurior. Wingless (“ergatoid”) males never leave their maternal colony and fight remorselessly among each other for the access to emerging females. The peaceful winged males disperse after about 10 days, but beforehand also mate in the nest. In the first 5 days of their life, winged males perform a chemical female mimicry that protects them against attack and even makes them sexually attractive to ergatoid males. When older, the chemical profile of winged males no longer matches that of virgin females; nevertheless, they are still tolerated, which so far has been puzzling. Contrasting this general pattern, we have identified a single aberrant colony in which all winged males were attacked and killed by the ergatoid males. A comparative analysis of the morphology and chemical profile of these untypical attacked winged males and the tolerated males from several normal colonies revealed that normal old males are still performing some chemical mimicry to the virgin queens, though less perfect than in their young ages. The anomalous attacked winged males, on the other hand, had a very different odour to the females. Our study thus exemplifies that the analysis of rare malfunctioning can add valuable insight on functioning under normal conditions and allows the conclusion that older winged males from normal colonies of the ant C. obscurior are guarded through an imperfect chemical female mimicry, still close enough to protect against attacks by the wingless fighters yet dissimilar enough not to elicit their sexual interest.     

Procurement of exogenous ammonia by the swallowtail butterfly, Papilio polytes, for protein biosynthesis and sperm production

How to acquire sufficient quantity of nitrogen is a pivotal issue for herbivores, particularly for lepidopterans (butterflies and moths) of which diet quality greatly differs among their life stages. Male Lepidoptera often feed from mud puddles, dung, and carrion, a behavior known as puddling, which is thought to be supplementary feeding targeted chiefly at sodium. During copulation, males transfer a spermatophore to females that contains, besides sperm, nutrients (nuptial gifts) rich in sodium, proteins, and amino acids. However, it is still poorly understood how adults, mostly nectarivores, extract nitrogen from the environment. We examined the availability of two ubiquitous inorganic nitrogenous ions in nature, viz. ammonium (or ammonia) and nitrate ions, as nutrients in a butterfly, and show that exogenous ammonia ingested by adult males of the swallowtail, Papilio polytes, can serve as a resource for protein biosynthesis. Feeding experiments with ¹⁵N-labeled ammonium chloride revealed that nitrogen was incorporated into eupyrene spermatozoa, seminal protein, and thoracic muscle. Ammonia uptake by males significantly increased the number of eupyrene sperms in the reproductive tract tissues. The females also had the capacity to assimilate ammonia into egg protein. Consequently, it is evident that acquired ammonia is utilized for the replenishment of proteins allocable for reproduction and somatic maintenance. The active exploitation of exogenous ammonia as a nutrient by a butterfly would foster better understanding of the foraging and reproductive strategies in insects.     

Copulatory behavior in a pholcid spider: males use specialized genitalic movements for sperm removal and copulatory courtship

Sexual selection may operate on pre-copulatory, copulatory, and post-copulatory traits. An example of a copulatory target of sexual selection is the genitalic movements a male performs during copulation. These movements may function either to prevent sperm competition or to influence a female’s fertilization decision. Here we investigated how copulation duration, pedipalp movements, and abdominal movements that males of the pholcid spider Holocnemus pluchei produce during copulation influence sperm removal and/or patterns of successful sperm transfer. We compared mating events with virgin and mated females for differences in copulatory and post-copulatory behavior. We expected longer copulation duration, longer pedipalp movement duration, and more complex and frequent pedipalp and abdominal movements when males mated with mated females compared to virgin females. Except for abdominal movements, our results corroborated these predictions. Furthermore, when we investigated mating events with mated females, we observed sperm mass ejection from the female gonopore and physical removal of sperm by males’ procursi. Females with interrupted second mating events showed a significant reduction of stored sperm masses compared to females with completed mating events. We suggest that males use alternating pedipalp movements to remove most of the rival sperm stored by mated females prior to sperm transfer. Copulation duration and pedipalp movements can be further used to transfer sperm and/or as a form of genitalic copulatory courtship.     

Diel periodicity of pheromone release by females of Planococcus citri and Planococcus ficus and the temporal flight activity of their conspecific males

The diel periodicity of sex pheromone release was monitored in two mealybug species, Planococcus citri and Planococcus ficus (Hemiptera; Pseudococcidae), using sequential SPME/GCMS analysis. A maximal release of 2 ng/h pheromone by 9–12-day-old P. citri females occurred 1–2 h before the beginning of photophase. The highest release of pheromone by P. ficus females was 1–2 ng/2 h of 10–20-day-old females, approximately 2 h after the beginning of photophase. Mating resulted in termination of the pheromone release in both mealybug species. The temporal flight activity of the males was monitored in rearing chambers using pheromone baited delta traps. Males of both P. citri and P. ficus displayed the same flight pattern and began flying at 06:00 hours when the light was turned on, reaching a peak during the first and second hour of the photophase. Our results suggest that other biparental mealybug species display also diel periodicities of maximal pheromone release and response. Direct evaluation of the diel periodicity of the pheromone release by the automatic sequential analysis is convenient and will be very helpful in optimizing the airborne collection and identification of other unknown mealybug pheromones and to study the calling behavior of females. Considering this behavior pattern may help to develop more effective pheromone-based management strategies against mealybugs.     

Biogenic amine levels, reproduction and social dominance in the queenless ant Streblognathus peetersi

Social harmony often relies on ritualised dominance interactions between society members, particularly in queenless ant societies, where colony members do not have developmentally predetermined castes but have to fight for their status in the reproductive and work hierarchy. In this behavioural plasticity, their social organisation resembles more that of vertebrates than that of the “classic” social insects. The present study investigates the neurochemistry of the queenless ant species, Streblognathus peetersi, to better understand the neural basis of the high behavioural plasticity observed in queenless ants. We report measurements of brain biogenic amines [octopamine, dopamine, serotonin] of S. peetersi ants; they reveal a new set of biogenic amine influences on social organisation with no common features with other “primitively organised societies” (bumble bees) and some common features with “highly eusocial” species (honey bees). This similarity to honey bees may either confirm the heritage of queenless species from their probably highly eusocial ancestors or highlight independent patterns of biogenic amine influences on the social organisation of these highly derived species.     

Effects of soil types and cultural practices on the fire ant,Solenopsis invicta,in sugarcane

A two-year study (1984, 1985) conducted in South Louisiana sugarcane fields to investigate the effects of selected soil types and cultural practices on the abundance of the fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), showed that the highest S. invicta populations were present in clayey fields. There was a several-fold difference in the number of S. invicta mounds between the early-harvested fields and late-harvested or plant fields. Additionally, S. invicta mounds were more abundant in fields where there was a greater amount of ground cover (weeds and crop residues). During the 1984 study, foraging by S. invicta on clayey soils was somewhat lower in harvested than in planted fields. However, there was a trend for higher foraging in harvested than in planted fields in 1985. Significantly higher amounts of phosphorus, potassium, calcium, magnesium, sodium and percent organic matter were found in clayey than in sandy fields during 1984 and 1985. The significantly higher moisture content and the lower bulk density in clayey than in sandy soils seemed potentially conducive to greater S. invicta abundance through elimination of the risk of colony desiccation, as well as enhancement of subterranean foraging tunnels and deeper colony expansion.     

Vision-independent odometry in the ant Cataglyphis cursor

In contrast to flying insects, in which distance estimation is visually mediated, self-induced image motion and use of familiar landmarks are known to play a minor role in ants. Here we show that strictly diurnal Cataglyphis cursor ants can gauge with accuracy the distance they have travelled even in complete darkness in the absence of any other cues, i.e. chemical or protocounting information. Thus, an ants odometer is a vision-independent system based on proprioceptive cues, implicating some form of step counting, which remain to be elucidated.     

Gamergates in the Australian ant subfamily Myrmeciinae

Ant workers can mate and reproduce in a few hundreds of species belonging to the phylogenetically basal poneromorph subfamilies (sensu Bolton 2003). We report the first occurrence of gamergates (i.e. mated reproductive workers) in a myrmeciomorph subfamily. In a colony of Myrmecia pyriformis that was collected without a queen, workers continued to be produced over a period of 3 years in the laboratory. Behavioural observations and ovarian dissections indicated that three workers were mated and produced the diploid offspring. The Myrmeciinae are thus another taxon in which the selective benefits of sexual reproduction by workers can be investigated.     

接种丛枝菌根真菌对雌雄美洲黑杨吸收铅镉的影响

以雌雄美洲黑杨(Populus deltoides)为研究对象,砂培条件下,研究接种丛枝菌根真菌(Glomus intraradices)对受Pb污染(200 mg·kg-1)、Cd污染(10 mg·kg-1)及复合污染的雌雄美洲黑杨Pb和Cd的富集与分配特征的影响,关注Pb/Cd复合污染独特的环境效应.结果表明:1未接种丛枝菌根真菌条件下,与单一污染相比,复合污染增加了美洲黑杨雄株叶、粗根、细根Pb和Cd含量;复合污染增加了雌株叶片中Pb和Cd含量,却降低了粗根和细根中Pb和Cd含量;复合污染条件下雄株Pb和Cd向地上部分器官的迁移率分别增加135%和78%,雌株则分别增加52%和18%.2复合污染条件下,接种丛枝菌根真菌引起雄株Pb和Cd富集系数分别增加87%和6%,雌株则分别增加171%和65%;雄株Pb和Cd向地上部分器官的迁移率降低65%和69%,雌株则分别降低59%和53%.3Pb污染条件下,接种丛枝菌根真菌的雌雄之间Pb积累量没有显著差异;Cd污染条件下,接种丛枝菌根真菌的雄株总Cd积累量是雌株的1.7倍;复合污染条件下,接种丛枝菌根真菌的雌株Pb和Cd总积累量分别是雄株的1.3和1.2倍.本研究表明,接种G.intraradices能提高美洲黑杨的Pb和Cd积累能力,对于不同污染条件下,应根据实际情况选择合适的杨树性别进行造林和生态修复.     

Potential economic impact of introduction and spread of the red imported fire ant, Solenopsis invicta, in Hawaii

Globally, many invasive alien species have caused extensive ecological and economic damage from either accidental or intentional introduction. The red imported fire ant, Solenopsis invicta, has created billions of dollars in costs annually, spreading as an invasive species across the southern United States. In 1998, the red imported fire ant spread into California creating a highly probable future introduction via shipped products to Hawaii. This paper presents the estimation of potential economic impacts of the red imported fire ant (RIFA) to the state of Hawaii. Evaluation of impacts focuses on the economic sectors of (1) households, (2) agriculture (cattle and crop production), (3) infrastructure (cemeteries, churches, cities, electrical, telephone, and cable services, highways, hospitals and schools), (4) recreation, tourism and business (hotels/resort areas, golf courses, commercial businesses and tourists), and (5) government expenditures (with minimal intervention). The full annual economic costs of the red imported fire ant to Hawaii are estimated (in US$ 2006) to be $211 million/year, comprised of $77 million in damages and expenditures and $134 million in foregone outdoor opportunities to households and tourists. The present value of the projected costs of RIFA over a 20-year period after introduction total $2.5 billion. RIFA invasions across the globe indicate that economic cost-effective action in Hawaii entails implementation of prevention, early detection and rapid response treatment programs for RIFA.     

Pheromone communication and the mushroom body of the ant, Camponotus obscuripes (Hymenoptera: Formicidae)

Communication by means of pheromones plays predominant roles in colony integration by social insects. However, almost nothing is known about pheromone processing in the brains of social insects. In this study, we successfully applied intracellular recording and staining techniques to anatomically and physiologically characterize brain neurons of the ant Camponotus obscuripes. We identified 42 protocerebral neurons that responded to undecane and/or formic acid, components of alarm pheromones that evoke attraction or evasive behavior, respectively. Notably, 30 (71%) of these neurons were efferent (output) or feedback neurons of the mushroom body, and many of these exhibited different responses to formic acid and undecane. Eight of the remaining 12 neurons had arborizations in the lateral and/or medial protocerebrum, which receive terminations of efferent neurons of the mushroom body and from which premotor descending neurons originate. The remaining four neurons were bilateral neurons that connect lateral accessory lobes or dorsal protocerebrums of both hemispheres. We suggest that the mushroom body of the ant participates in the processing of alarm pheromones. Seventeen (40%) of 42 neurons exhibited responses to nonpheromonal odors, indicating that the pheromonal and nonpheromonal signals are not fully segregated when they are processed in the protocerebrum. This may be related to modulatory functions of alarm pheromones, i.e., they change alertness of the ant and change responses to a variety of sensory stimuli.