Charting uncertainty about ant origins.
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Animals↗
Biomedical subjects
Ross H Crozier
Publications and source records attributed to Ross H Crozier.
Phylogenetic analysis of honey bee behavioral evolution.
DNA sequences from three mitochondrial (rrnL, cox2, nad2) and one nuclear gene (itpr) from all 9 known honey bee species (Apis), a 10th possible species, Apis dorsata binghami, and three outgroup species (Bombus terrestris, Melipona bicolor and Trigona fimbriata) were used to infer Apis phylogenetic relationships using Bayesian analysis. The dwarf honey bees were confirmed as basal, and the giant and cavity-nesting species to be monophyletic. All nodes were strongly supported except that grouping Apis cerana with A. nigrocincta. Two thousand post-burnin trees from the phylogenetic analysis were used in a Bayesian comparative analysis to explore the evolution of dance type, nest structure, comb structure and dance sound within Apis. The ancestral honey bee species was inferred with high support to have nested in the open, and to have more likely than not had a silent vertical waggle dance and a single comb. The common ancestor of the giant and cavity-dwelling bees is strongly inferred to have had a buzzing vertical directional dance. All pairwise combinations of characters showed strong association, but the multiple comparisons problem reduces the ability to infer associations between states between characters. Nevertheless, a buzzing dance is significantly associated with cavity-nesting, several vertical combs, and dancing vertically, a horizontal dance is significantly associated with a nest with a single comb wrapped around the support, and open nesting with a single pendant comb and a silent waggle dance.
Animals↗
The evolution of worker caste diversity in social insects.
Morphological diversification of workers is predicted to improve the division of labor within social insect colonies, yet many species have monomorphic workers. Individual-level selection on the reproductive capacities of workers may counter colony-level selection for diversification, and life-history differences between species (timing of caste determination, colony size, genetic variation available) may mediate the strength of this selection. We tested this through phylogenetically independent contrast analyses on a new data set for 35 ant species. Evidence was found that early divergence of queen-worker developmental pathways may facilitate the evolution of worker diversity because queen-worker dimorphism was strongly positively associated with diversity. By contrast, risks for colonies that invest in specialized workers and colony size effects on costs of worker reproduction seem unlikely to strongly affect the evolution of worker diversity because there was no significant association between colony size and diversity when controlling statistically for queen-worker dimorphism. Finally, worker diversity was greater in species with multiple lineages per colony, and it was negatively associated with relatedness in monogynous species. This could be due to high intracolonial genetic variance favoring the expression and evolution of great worker diversity or to diversity evolving more easily when there is selection for repression of worker reproduction (worker policing).
Animals↗
Phylogenetic relationships among species groups of the ant genus Myrmecia.
Phylogenetic relationships among the nine species groups of the predominately Australian ant genus Myrmecia were inferred using 38 Myrmecia species and an outgroup using DNA sequences from two nuclear genes (622nt from 28S rRNA and 1907nt from the long-wave opsin gene). Nothomyrmecia macrops was selected as the most appropriate outgroup based on recent reliable studies showing monophyly of Myrmecia with Nothomyrmecia. The four species groups with an occipital carina (those of gulosa, nigrocincta, urens, and picta) were found to form a paraphyletic and basal assemblage out of which the five species groups lacking an occipital carina (those of aberrans, mandibularis, tepperi, cephalotes, and pilosula) arise as a strongly supported monophyletic assemblage. Monophyly was supported for four groups (those of gulosa, nigrocincta, picta, and mandibularis) but the situation is unclear for four others (those of urens, aberrans, tepperi, and pilosula). The aberrans group appears to be basal within the group lacking an occipital carina; a previous suggestion that it is the sister group to the rest of the genus is thus not supported.
Animals↗
Age determination in individual wild-caught Drosophila serrata using pteridine concentration.
Fluorescence spectrophotometry can reliably detect levels of the pteridine 6-biopterin in the heads of individual Drosophila serrata Malloch 1927. Pteridine content in both laboratory and field captured flies is typically a level of magnitude higher than the minimally detectable level (mean(lab)=0.54 units, mean(field)=0.44 units, minimum detectable level=0.01 units) and can be used to predict individual age in laboratory populations with high certainty (r2=57%). Laboratory studies of individuals of known age (from 1 to 48 days old) indicate that while pteridine level increases linearly with age, they also increase in a linear manner with rearing temperature and ambient light levels, but are independent of sex. As expected, the longevity of laboratory-reared males (at least 48 days) is higher than the range of predicted ages of wild-caught males based on individual pteridine levels (40 days). However, the predictive equation based on pteridine level alone suggested that a number of wild-caught males were less than 0 days old, and the 95% confidence limits for these predictions based on the inverse regression are broad. The age of the oldest wild-caught male is predicted to fall within the range of 2 to 50 days. The significant effects of temperature and light intensity determined in the laboratory study (effect sizes omega2=14.3 and 20.4%, respectively) suggests that the calibration of the age prediction equation for field populations would be significantly improved when combined with fine-scaled studies of habitat temperature and light conditions. The ability to determine relative age in individual wild-caught D. serrata presents great opportunities for a variety of evolutionary studies on the dynamics of natural populations.
Aging↗
Variation in positive selection in termite GNBPs and Relish.
Social insects are model organisms for investigating molecular evolution in the innate immune system. Their diversity affords comparative analysis among closely related species, and group living is likely to contribute to the pathogen stress imposed on the immune system. We used different models of nucleotide substitution at nonsynonymous (amino acid altering) and synonymous (silent) sites to compare the different levels and type of selection among three immunity genes in 13 Australian termite species (Nasutitermes). The immunity genes include two encoding pathogen recognition proteins (gram-negative bacterial-binding proteins) that duplicated and diverged before or soon after the evolution of the termites and a transcription factor (Relish), which induces the production of antimicrobial peptides. A comparison of evolutionary models that assign four unrestricted classes of dN/dS (the ratio of the nonsynonymous to synonymous substitution rate) to different Nasutitermes lineages revealed that the occurrence of positive selection (dN/dS > 1) varies among lineages and the three genes. Positive selection appears to have driven the evolution of all three genes in an ancestral lineage of three subterranean termites. It had previously been suggested that there was a transition along this ancestral lineage to termite morphology and ecology associated with a diet of decayed wood, a diet that may expose termites to elevated levels of fungal and bacterial pathogens. Relish appears to have experienced the highest levels of selective pressure for change among all three genes. Positively selected sites in the molecule are located in regions that are important for its activation, which suggests that amino acid substitutions at these sites are a counter response to pathogen mechanisms that disrupt the activation of Relish.
Amino Acid Substitution↗
Single nucleotide +1 frameshifts in an apparently functional mitochondrial cytochrome b gene in ants of the genus Polyrhachis.
Twelve of 30 species examined in the ant genus Polyrhachis carry single nucleotide insertions at one or two positions within the mitochondrial cytochrome b (cytb) gene. Two of the sites are present in more than one species. Nucleotide substitutions in taxa carrying insertions show the strong codon position bias expected of functional protein coding genes, with substitutions concentrated in the third positions of the original reading frame. This pattern of evolution of the sequences strongly suggests that they are functional cytb sequences. This result is not the first report of +1 frameshift insertions in animal mitochondrial genes. A similar site was discovered in vertebrates, where single nucleotide frameshift insertions in many birds and a turtle were reported by Mindell et al. (Mol Biol Evol 15:1568, 1998). They hypothesized that the genes are correctly decoded by a programmed frameshift during translation. The discovery of four additional sites gives us the opportunity to look for common features that may explain how programmed frameshifts can arise. The common feature appears to be the presence of two consecutive rare codons at the insertion site. We hypothesize that the second of these codons is not efficiently translated, causing a pause in the translation process. During the stall the weak wobble pairing of the tRNA bound in the peptidyl site of the ribosome, together with an exact Watson-Crick codon-anticodon pairing in the +1 position, allows translation to continue in the +1 reading frame. The result of these events is an adequate level of translation of a full-length and fully functional protein. A model is presented for decoding of these mitochondrial genes, consistent with known features of programmed translational frameshifting in the yeast TY1 and TY3 retrotransposons.
Amino Acid Sequence↗
Molecular phylogeny of the benthic shallow-water octopuses (Cephalopoda: Octopodinae).
Octopus has been regarded as a "catch all" genus, yet its monophyly is questionable and has been untested. We inferred a broad-scale phylogeny of the benthic shallow-water octopuses (subfamily Octopodinae) using amino acid sequences of two mitochondrial DNA genes: Cytochrome oxidase subunit III and Cytochrome b apoenzyme, and the nuclear DNA gene Elongation Factor-1alpha. Sequence data were obtained from 26 Octopus species and from four related genera. Maximum likelihood and Bayesian approaches were implemented to estimate the phylogeny, and non-parametric bootstrapping was used to verify confidence for Bayesian topologies. Phylogenetic relationships between closely related species were generally well resolved, and groups delineated, but the genes did not resolve deep divergences well. The phylogenies indicated strongly that Octopus is not monophyletic, but several monophyletic groups were identified within the genus. It is therefore clear that octopodid systematics requires major revision.
Amino Acid Sequence↗
Duplication and diversifying selection among termite antifungal peptides.
We have identified and analyzed the mRNA sequence of 20 new defensin-like peptides from 11 Australian termite species of Nasutitermes and from an outgroup, Drepanotermes rubriceps. The sequence was amplified by reverse transcriptase PCR with a degenerate primer designed from termicin, an antifungal peptide previously characterized from the termite Pseudocanthotermes spiniger. All 20 genes show high sequence identity with P. spiniger termicin and have duplicated repeatedly during the radiation of Nasutitermes. Comparison of the relative fixation rates of synonymous (silent) and nonsynonymous (amino acid altering) mutations indicates that the Nasutitermes termicins are positively selected. This positive selection appears to drive a decrease in termicin charge. In termites with two genes, the decrease in charge is predominantly restricted to one termicin. Furthermore, the spread of charge is significantly greater within species than across species among amino acid sites that appear to be under strong positive selection and this spread is attributable to only three sites. Our results suggest that after termicin duplication, certain critical sites have maintained a positive charge in one duplicate and evolved towards neutrality in the other and that positive selection has directed these changes repeatedly and independently. This diversification among duplicated genes may be a counter-response to the evolution of fungal resistance in social insects that are particularly vulnerable to fungal epidemics.
Amino Acid Sequence↗
Mating system and population structure of the primitively eusocial wasp Ropalidia revolutionalis: a model system for the evolution of complex societies.
Mating systems are important determinants of genetic structure in cooperative groups, and their effects can influence profoundly the interactions of group members. The primitively eusocial wasp, Ropalidia revolutionalis, has an interesting genetic and social structure that makes it an excellent model system for examining the evolution of more complex societies. In particular, its colonies sometimes have multiple queens, a key characteristic of more advanced wasp societies. In this study, we have characterized the mating system of the social wasp Ropalidia revolutionalis to understand better its colony genetic structure. R. revolutionalis females nearly always mate singly and they are unrelated to their mates. However, different females in the same colony do mate with males, on average, who are related as cousins. Single mating will help to maintain high relatedness, which should be important for continued cooperation in multiple queen societies, but it creates potential conflicts in single queen colonies over the production of males as well as over the timing of male production. We have also characterized the population structure of R. revolutionalis from Townsville, in tropical north Queensland, to Brisbane in the subtropics. Even at such a large scale, the population is remarkably unstructured with an average F(ST) of 0.0546. There is weak isolation by distance, and evidence for subtle differentiation between a southern region with no dry season, which extends as far north as Rockhampton, and a northern region with a severe to moderate dry season. This may reflect historical effects of extreme aridity on the population structure.
Analysis of Variance↗
A tree island approach to inferring phylogeny in the ant subfamily Formicinae, with especial reference to the evolution of weaving.
The ant subfamily Formicinae is a large assemblage (2458 species (J. Nat. Hist. 29 (1995) 1037), including species that weave leaf nests together with larval silk and in which the metapleural gland-the ancestrally defining ant character-has been secondarily lost. We used sequences from two mitochondrial genes (cytochrome b and cytochrome oxidase 2) from 18 formicine and 4 outgroup taxa to derive a robust phylogeny, employing a search for tree islands using 10000 randomly constructed trees as starting points and deriving a maximum likelihood consensus tree from the ML tree and those not significantly different from it. Non-parametric bootstrapping showed that the ML consensus tree fit the data significantly better than three scenarios based on morphology, with that of Bolton (Identification Guide to the Ant Genera of the World, Harvard University Press, Cambridge, MA) being the best among these alternative trees. Trait mapping showed that weaving had arisen at least four times and possibly been lost once. A maximum likelihood analysis showed that loss of the metapleural gland is significantly associated with the weaver life-pattern. The graph of the frequencies with which trees were discovered versus their likelihood indicates that trees with high likelihoods have much larger basins of attraction than those with lower likelihoods. While this result indicates that single searches are more likely to find high- than low-likelihood tree islands, it also indicates that searching only for the single best tree may lose important information.
Animals↗
Isolation and characterization of a termite transferrin gene up-regulated on infection.
PCR-based subtractive hybridization was used to isolate genes preferentially expressed in a termite (Mastotermes darwiniensis) following exposure to an entomopathogenic fungus. The subtraction procedure yielded a cDNA clone encoding a putative transferrin that, when sequenced to its ends, is the largest (728 amino acids) for any insect transferrin characterized to date. Cysteines and residues comprising putative iron-binding sites are conserved in both N- and C-terminal lobes, suggesting structural and functional similarity to diferric vertebrate transferrins. A quantitative PCR assay confirmed a significant increase in transferrin expression following infection, suggesting its up-regulation is part of the innate immune response. However, codon-based tests for selection among known insect transferrins revealed only a small proportion of codon-sites positively selected. Thus, unlike certain vertebrate transferrin lineages, no widespread evidence for pathogen-mediated positive selection was detected at this locus.
Amino Acid Sequence↗
The evolution of parasites from their hosts: intra- and interspecific parasitism and Emery's rule.
In some taxa of Hymenoptera, fungi, red algae and mistletoe, parasites and their hosts are either sibling species or at least closely related (Emery's rule). Three evolutionary mechanisms have been proposed for this phenomenon: (i) intraspecific parasitism is followed by sympatric speciation; (ii) allopatric speciation is followed by secondary sympatry and the subsequent parasitism of one sibling species by the other; and (iii) allopatric speciation of a species with intraspecific parasitism is followed by secondary sympatry, in which one species becomes an obligate parasite of the other. Mechanisms (i) and (ii) are problematic, while mechanism (iii) has not, to our knowledge, been analysed quantitatively. In this paper, we develop a model for single- and two-species evolutionary stable strategies (ESSs) to examine the basis for Emery's rule and to determine whether mechanism (iii) is consistent with ESS reasoning. In secondary sympatry after allopatric speciation, the system's evolution depends on the relative abundances of the two sibling species and on the proportional damage wrought by parasites of each species on non-parasitic members of the other. Depending on these interspecific effects, either the rarer or the commoner species may become the parasite and the levels of within-species parasitism need not determine which evolves to obligate parasitism.
Animals↗
Daughters inherit colonies from mothers in the 'living-fossil' ant Nothomyrmecia macrops.
Newly mated queens of monogynous (single queen) ants usually found their colonies independently, without the assistance of workers. In polygynous (multiple queen) species queens are often adopted back into their natal nest and new colonies are established by budding. We report that the Australian 'living-fossil' ant, Nothomyrmecia macrops, is exceptional in that its single queen can be replaced by one of the colony's daughters. This type of colony founding is an interesting alternative reproductive strategy in monogynous ants, which maximizes fitness under kin selection. Successive queen replacement results in a series of reproductives over time (serial polygyny), making these colonies potentially immortal. Workers raise nieces and nephews (relatedness < or = 0.375) the year after queen replacement. Although N. macrops is 'primitive' in many other respects, colony inheritance is likely to be a derived specialization resulting from ecological constraints on solitary founding.
Animals↗
Pheromones and the single queen.
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Aggression↗
Population and colony genetic structure of the primitive termite Mastotermes darwiniensis.
The termite Mastotermes darwiniensis is the sole extant member of its family and occupies the basal position in the phylogeny of the eusocial order Isoptera. In this study, we investigated the micro- and macrogeographic genetic structure of M. darwiniensis in its native range in Australia. A total of 1591 workers were sampled from 136 infested trees in 24 locales. Each locale was separated by 2-350 km, and these locales were found within two broader geographic regions approximately 1500 km apart. The multilocus genotypes of all termites were assayed at six polymorphic microsatellite loci. The genetic data indicated that colonies typically fed on multiple trees within locales and extended over linear distances of up to 320 m. Single colonies were frequently headed by multiple reproductives. Workers were highly related (r = 0.40) and substantially inbred (f = 0.10). Thus, M. darwiniensis colonies are characterized by the input of alleles from multiple reproductives, which sometimes engage in consanguineous matings. Our analyses of population genetic structure above the level of the colony indicated that locales and regions were significantly differentiated (theta(locale) = 0.50, theta(region) = 0.37). Moreover, locales showed a pattern of genetic isolation by distance within regions. Thus, M. darwiniensis populations display restricted gene flow over moderate geographic distances. We suggest that the genetic patterns displayed by M. darwiniensis result primarily from selective pressures acting to maintain high relatedness among colonymates while allowing colonies to grow rapidly and dominate local habitats.
Animals↗