Benefits and costs of secondary polygyny in the dampwood termite Zootermopsis angusticollis

Newly molted female neotenic reproductives of the dampwood termite Zootermopsis angusticollis Hagen were allowed to mature in the presence of a neotenic male, a fixed number of larval helpers, and varying numbers of sibling neotenic queens to assess the impact of secondary polygyny to the individual and colony. Under monogyne conditions, neotenics developed more ovarioles per ovary and had higher individual fecundities after 60 d compared with females under polygyne conditions. Queens in groups of three females were able to gain more body mass than those in groups of five. Although the division of resources provided by helpers reduced individual female development and fecundity under polygyne conditions, it resulted in an overall increase in colony fecundity. In addition, neotenic females in polygynous colonies did not differ significantly in reproductive competence. There was no evidence that neotenics were attacked or injured by other reproductives or larval helpers, suggesting little if any reproductive competition among sibling queens. The physiological responses of neotenics to the increasing queen/worker ratio may have the benefit of enhancing the colony growth at the cost of the fecundity of individual queens.     

Immunity and reproduction during colony foundation in the dampwood termite, Zootermopsis angusticollis

Abstract.  Termite primary reproductives may be exposed to pathogens when dispersing from their parental nest and establishing a new colony. Immunity and reproduction are investigated during colony foundation by implanting a nylon filament into the abdomen of mated and unmated female and male primary reproductives of the dampwood termite Zootermopsis angusticollis. Primary reproductives are paired in combinations of female/male, female/female and male/male and, using confocal microscopy, immune defence is assessed by measuring the degree of encapsulation of nylon implants during three periods of colony foundation: (I) shortly after pairing; (II) during copulation/oocyte maturation; and (III) during oviposition. There are differences in the encapsulation response of mated and unmated termites that are contingent on the period of colony foundation when termites are challenged. Mated females and males have significantly greater encapsulation responses than their unmated counterparts shortly after pairing, perhaps as a prophylactic measure against exposure to disease. The encapsulation response of mated and unmated males does not differ significantly during periods II and III. The onset of oviposition is significantly delayed in mated females that received implants during periods I and II. Mated females have a significantly reduced encapsulation response during the time of copulation and oocyte maturation, but not during oviposition. Overall, males have a significantly greater ability than females to encapsulate a nylon implant. The findings suggest that reproduction can reduce the immune response in female primary reproductives. The results are discussed in light of trade-offs between immunity and reproduction during the critical life-history phase of colony establishment in termites.     

The cellulolytic system of the termite gut

The demand for the usage of natural renewable polymeric material is increasing in order to satisfy the future needs for energy and chemical precursors. Important steps in the hydrolysis of polymeric material and bioconversion can be performed by microorganisms. Over about 150 million years, termites have optimized their intestinal polysaccharide-degrading symbiosis. In the ecosystem of the “termite gut,” polysaccharides are degraded from lignocellulose, such as cellulose and hemicelluloses, in 1 day, while lignin is only weakly attacked. The understanding of the principles of cellulose degradation in this natural polymer-degrading ecosystem could be helpful for the improvement of the biotechnological hydrolysis and conversion of cellulose, e.g., in the case of biogas production from natural renewable plant material in biogas plants. This review focuses on the present knowledge of the cellulose degradation in the termite gut.     

Endocrine effects of social stimuli on maturing queens of the dampwood termite Zootermopsis angusticollis

Abstract.  The reproductive physiology of social insects is often highly responsive to social stimuli from nestmates, but the mechanisms underlying this sensitivity are usually poorly understood. The effect of varied social conditions on the endocrinology and ovarian maturation in maturing female primary reproductives of the dampwood termite Zootermopsis angusticollis Hagen is studied to better understand their developmental responses to conspecifics. Newly dealate queens are paired with a reproductive male, with another maturing female, or are allowed to mature in isolation. Developmental responses are tracked by monitoring rates of juvenile hormone (JH) production by corpora allata in vitro , haemolymph ecdysteroids titres and ovarian development after 5, 10, 15 and 30 days of maturation. Significant declines in rates of JH production rates are observed by days 5, 10 and 30, respectively, for females paired with males, left to mature in isolation or paired with a female. Ecdysteroid titres increase by day 5 and stay elevated in females nesting with males. By contrast, for CA from females that are isolated or paired with another female, the titres decline and stay low until at least day 15, but increase significantly by day 30. These hormonal differences correspond to differential rates of physiological maturation, with more rapid ovarian development occurring in females paired with a male, than in those nesting alone or with another female. The results suggest that JH and ecdysteroids modulate the ovarian response of alates to stimuli from nestmates during this period of maturation, and that JH and ecdysteroid titres may be regulated independently during this period of development.     

Susceptibility and behavioral responses of the dampwood termite Zootermopsis angusticollis to the entomopathogenic nematode Steinernema carpocapsae

Termites exploit microbially rich resources such as decayed wood and soil that are colonized by potentially pathogenic and parasitic fungi, bacteria, viruses, and nematodes. In colonies composed of thousands of individuals, the risk of infection among nestmates is significant, and individual and social behavior could involve various adaptations to resist disease and parasitism. Here we show that the dampwood termite Zootermopsis angusticollis (Hagen) exhibits a dosage dependent susceptibility to the soil nematode Steinernema carpocapsae (Weiser) (Mexican strain) and that this social insect significantly alters its behavior in response to this entomopathogenic roundworm. Relative to their baseline behavior, termites exposed to infective juveniles increased the frequency and duration of allogrooming and vibratory displays as well as two other novel behaviors, abdominal tip-raising and self-scratching. Whereas the first two behaviors likely reflect general adaptations to reduce susceptibility to a variety of pathogens and parasites, the latter behaviors might be specific to nematodes because they have never been observed in Z. angusticollis in any other pathogenic context. Our results support the hypotheses that behavioral responses in termites are important in the control of pathogenic and parasitic microorganisms and that termite susceptibility is socially mediated.     

Extracting DNA from the gut microbes of the termite (Zootermopsis nevadensis)

Termites are among the few animals known to have the capacity to subsist solely by consuming wood. The termite gut tract contains a dense and species-rich microbial population that assists in the degradation of lignocellulose predominantly into acetate, the key nutrient fueling termite metabolism (Odelson & Breznak, 1983). Within these microbial populations are bacteria, methanogenic archaea and, in some ("lower") termites, eukaryotic protozoa. Thus, termites are excellent research subjects for studying the interactions among microbial species and the numerous biochemical functions they perform to the benefit of their host. The species composition of microbial populations in termite guts as well as key genes involved in various biochemical processes has been explored using molecular techniques (Kudo et al., 1998; Schmit-Wagner et al., 2003; Salmassi & Leadbetter, 2003). These techniques depend on the extraction and purification of high-quality nucleic acids from the termite gut environment. The extraction technique described in this video is a modified compilation of protocols developed for extraction and purification of nucleic acids from environmental samples (Mor et al., 1994; Berthelet et al., 1996; Purdy et al., 1996; Salmassi & Leadbetter, 2003; Ottesen et al. 2006) and it produces DNA from termite hindgut material suitable for use as template for polymerase chain reaction (PCR).     

Hemicellulose-degrading bacteria and yeasts from the termite gut

Termites play a major role in the recycling of photosynthetically fixed carbon. With the aid of their symbiotic intestinal flora, they are able to degrade extensively wood constituents such as cellulose and hemicellulose. Nevertheless, the microbial species involved in the degradation of hemicelluloses are poorly defined. The purpose of this paper was to examine the microflora involved in hemicellulose degradation. Different aerobic and facultatively anaerobic bacteria and yeasts were isolated using xylan, arabinogalactan and carboxymethylcellulose as substrates. Gram-positive isolates belonged to the genera Bacillus, Paenibacillus, Streptomyces or the actinobacteria group, while the Gramnegative strains were assigned to the genera Pseudomonas, Acinetobacter, Ochrobactrum , and to genera belonging to the family Enterobacteriaceae. The spectrum and activity of xylan- and arabinogalactan-hydrolysing glycosidases of these new isolates, together with additional bacterial strains originally obtained from enrichments with aromatic compounds were determined.     

Social influence of larvae on ovarian maturation in primary and secondary reproductives of the dampwood termite Zootermopsis angusticollis

We tested the effect of larvae on the reproductive maturation and fecundity of female primary and secondary reproductives of the termite Zootermopsis angusticollis Hagen (Isoptera; Termopsidae) by varying the number of third‐ to fourth‐instar larvae nesting with heterosexually paired reproductives. Primary females had higher fecundities and oviposited sooner when nesting with larvae than females lacking larvae, but gained less body mass and had fewer functional ovarioles per ovary. Secondary reproductives nesting with larvae also had higher fecundities and oviposited sooner, but unlike primaries, they gained more body mass and had more functional ovarioles when larvae were present. The specific response of both primary and secondary females varied according to the number of larvae present. These results suggest that larvae can enhance the fecundity of primary and secondary females. Larvae may increase the energetic reserves of reproductives by performing colony labour, reducing pathogen load and providing trophallactic secretions. Trophallaxis with larvae may significantly enhance endogenous nitrogen, which is a limiting nutrient for termites. Primary females, which normally need to produce a first brood quickly to initiate a new colony, may expend limited nutritional resources on oogenesis rather than producing additional ovarioles. Primaries may also store fewer energetic reserves for long‐term brood care, and therefore gained less mass when larvae were present to attend to non‐reproductive tasks. Secondary females may exhibit a greater positive response to larvae than primaries because they begin reproductive life with fewer stored resources and thus their development and fecundity are more dependent on assistance from larvae. Both primary and secondary reproductives may become more dependent on the contributions of larvae as their rate of egg production increases with subsequent bouts of oviposition.     

Influence of sex-specific stimuli on ovarian maturation in primary and secondary reproductives of the dampwood termite Zootermopsis angusticollis

Abstract. It was hypothesized that female primary and secondary reproductives of the termite Zootermopsis angusticollis Hagen require sex-specific stimuli from a reproductive male to trigger ovarian maturation. To test this hypothesis, experimental laboratory colonies were established that contained female primary or secondary reproductives nesting: alone; with a male; with a female; and with three third- to fourth-instar larvae. Following colony initiation, we measured changes in body mass, ovariole number and fecundity over 60 days. Results indicate that the reproductive maturation of female primaries was promoted by contact with a male but inhibited by the presence of another female. Secondary females were not affected by the presence of another reproductive, regardless of sex, but the development of reproductive competency of primary females appeared to depend on male-specific stimulation. Reliance on male–female interaction to induce female reproductive development may ensure that the resources of newly dealate females are not wasted on producing larvae that would have a poor chance of surviving in the absence of a male. By contrast, secondary females maturing within established colonies are likely to have a mate and immediate assistance with non-reproductive tasks, and therefore do not delay ovarian maturation and reproduction until they perceive male-specific stimuli. These results demonstrate that male-specific stimuli affect only the reproductive development of primary females, and suggest that the degree to which primary and secondary females depend on mate assistance may have shaped their physiological responses to the presence of a reproductive male.     

Aerobic and facultatively anaerobic bacteria associated with the gut of Canada geese (Branta canadensis) and whistling swans (Cygnus columbianus columbianus)

Aerobic and facultatively anaerobic bacteria from the intestinal tracts of swans and geese were isolated and characterized as part of a larger study of the microbiological effects of migratory waterfowl on water quality. A total of 356 isolates were identified by using rapid identification methods and classified by using numerical taxonomy. A diverse population of bacteria was recovered from the waterfowl, and representative strains could be classified into 21 phena. The majority of the aerobic, heterotrophic bacteria found in the gut of the waterfowl were species of Enterobacteriaceae. Streptococcus. Lactobacillus, and Bacillus. Unfortunately, the birds that were examined did not harbor significant numbers of any waterfowl-specific bacterial species. Thus, it may not be possible to assess microbiological impact of migratory waterfowl by using and "indicator" species since avian fecal pollution could not be distinguished from animal and human fecal pollution.     

Interactions among cellulolytic bacteria from an anaerobic digester

High cellulolytic activity of particular strains did not cause dominance of one, or a few, species of fiber-digesting bacteria in a cattlewaste anaerobic digester. The population contained a large number of species and varieties with different cellulolytic and fiber-digesting activities. Although mixed cultures of some of these bacteria showed no intereffects, with others, cellulolysis was less or in some cases greater than that shown by individual components of the cultures. The interactions were probably related to effects on growth of the bacteria rather than on activities of components of the cellulase enzyme complex, and culture filtrates of two of the more numerous cellulolytic species ofClostridium affected growth of other cellulolytic bacteria. The inhibitory factor(s) appeared to be of bacteriocin type, but the stimulatory factor(s) was unknown. It was suggested that these interactions are localized or short-lived in the digester, and so the population remains in a dynamic steady state.Some inhibitions of growth of rumen cellulolytic bacteria were caused by the digester bacteria, but it was suggested that factors other than these inhibitions are responsible for the absence of rumen bacteria from anaerobic digesters.     

Dominant ectosymbiotic bacteria of cellulolytic protists in the termite gut also have the potential to digest lignocellulose

Wood‐feeding lower termites harbour symbiotic gut protists that support the termite nutritionally by degrading recalcitrant lignocellulose. These protists themselves host specific endo‐ and ectosymbiotic bacteria, functions of which remain largely unknown. Here, we present draft genomes of a dominant, uncultured ectosymbiont belonging to the order Bacteroidales, ‘Candidatus Symbiothrix dinenymphae’, which colonizes the cell surface of the cellulolytic gut protists Dinenympha spp. We analysed four single‐cell genomes of Ca. S. dinenymphae, the highest genome completeness was estimated to be 81.6–82.3% with a predicted genome size of 4.28–4.31 Mb. The genome retains genes encoding large parts of the amino acid, cofactor and nucleotide biosynthetic pathways. In addition, the genome contains genes encoding various glycoside hydrolases such as endoglucanases and hemicellulases. The genome indicates that Ca. S. dinenymphae ferments lignocellulose‐derived monosaccharides to acetate, a major carbon and energy source of the host termite. We suggest that the ectosymbiont digests lignocellulose and provides nutrients to the host termites, and hypothesize that the hydrolytic activity might also function as a pretreatment for the host protist to effectively decompose the crystalline cellulose components.     

Inbreeding and disease resistance in a social insect: effects of heterozygosity on immunocompetence in the termite Zootermopsis angusticollis

Recent research has shown that low genetic variation in individuals can increase susceptibility to infection and group living may exacerbate pathogen transmission. In the eusocial diploid termites, cycles of outbreeding and inbreeding characterizing basal species can reduce genetic variation within nestmates during the life of a colony, but the relationship of genetic heterogeneity to disease resistance is poorly understood. Here we show that, one generation of inbreeding differentially affects the survivorship of isolated and grouped termites (Zootermopsis angusticollis) depending on the nature of immune challenge and treatment. Inbred and outbred isolated and grouped termites inoculated with a bacterial pathogen, exposed to a low dose of fungal pathogen or challenged with an implanted nylon monofilament had similar levels of immune defence. However, inbred grouped termites exposed to a relatively high concentration of fungal conidia had significantly greater mortality than outbred grouped termites. Inbred termites also had significantly higher cuticular microbial loads, presumably due to less effective grooming by nestmates. Genetic analyses showed that inbreeding significantly reduced heterozygosity and allelic diversity. Decreased heterozygosity thus appeared to increase disease susceptibility by affecting social behaviour or some other group-level process influencing infection control rather than affecting individual immune physiology.     

Disease and colony establishment in the dampwood termite Zootermopsis angusticollis: survival and fitness consequences of infection in primary reproductives

Pathogens have likely infl uenced life-history evolution in social insects because their nesting ecology and sociality can exacerbate the risk of disease transmission and place demands on the immune system that ultimately can impact colony survival and growth. The costs of the maintenance and induction of immune function may be particularly significant in termites, which have a nitrogen-poor diet. We examined the effect of fungal exposure on survival and reproduction during colony foundation in the dampwood termite Zootermopsis angusticollis by experimentally pairing male and female primary reproductives and exposing them to single (‘acute’) and multiple (‘serial’) dosages of conidia of the fungus Metarhizium anisopliae and recording their survival and fitness over a 560 day period. The number of eggs laid 70 days post-pairing was significantly reduced relative to controls in the serial-exposure but not the acute-exposure treatment. Reproduction thus appeared to be more resilient to a single pathogen exposure than to serial challenge to the immune system. The impact of fungal exposure was transient: all surviving colonies had similar reproductive output after 300 days post-pairing. Our results suggest that disease can have significant survival and fitness costs during the critical phase of colony foundation but that infection at this time may not necessarily impact long-term colony growth. Received 25 February 2005; revised 27 September and 20 October 2005; accepted 20 December 2005.     

Endocrine changes in maturing primary queens of Zootermopsis angusticollis

Termite queens are highly specialized for reproduction, but little is known about the endocrine mechanisms regulating this ability. We studied changes in the endocrinology and ovarian maturation in primary reproductive females of the dampwood termite Zootermopsis angusticollis following their release from inhibitory stimuli produced by mature queens. Winged alates were removed from their natal nest, manually dewinged, then paired in an isolated nest with a reproductive male. Development was tracked by monitoring ovarian development, in vitro rates of juvenile hormone (JH) production by corpora allata, and hemolymph titers of JH and ecdysteroids. The production rate and titer of JH were positively correlated with each other but negatively correlated with ecdysteroid titer. Four days after disinhibition, JH release and titer decreased while ecdysteroid titer increased. The new levels persisted until day 30, after which JH increased and ecdysteroids decreased. Fully mature queens had the highest rates of JH production, the lowest ecdysteroid titers, and the greatest number of functional ovarioles. The results support the hypothesis that JH plays a dual role in termite queens depending on their stage of development; an elevated JH titer in immature alates may maintain reproductive inhibition, but an elevated JH titer in mature queens may stimulate ovarian activity. The decline in JH production and the elevation in ecdysteroid titer correspond to a period of physiological reorganization and activation. The specific function of ecdysteroids is unknown but they may help to modulate the activity of the corpora allata.