Evolution of eusociality and the soldier caste in termites: a validation of the intrinsic benefit hypothesis

In termites the evolution of reproductive altruism is not based on a particularly high relatedness between nestmates. For the evolution and maintenance of the ancestral sterile soldier caste, the benefits generated by the soldiers' presence must compensate the loss of the soldiers' reproductive potential. To study the impact of soldiers on colony's fitness, we manipulated the proportion of soldiers to nonsoldiers in colonies of the dry-wood termite Cryptotermes secundus.'Soldier-less' colonies were obtained by removing soldiers and inhibiting their development with an extract of soldier heads. The colonies were set up for 1 year in experimental nests in the field. 'Soldier-less' colonies produced fewer soldiers. The reduction of soldiers neither affected colony survival nor helper growth, but fewer dispersing sexuals were produced in 'soldier-less' than in control colonies. This confirms what was only supposed so far, that in termites soldiers are maintained for their intrinsic benefit to cost ratio.     

Geographic range size, life history and rates of diversification in Australian mammals

Abstract What causes species richness to vary among different groups of organisms? Two hypotheses are that large geographical ranges and fast life history either reduce extinction rates or raise speciation rates, elevating a clade's rate of diversification. Here we present a comparative analysis of these hypotheses using data on the phylogenetic relationships, geographical ranges and life history of the terrestrial mammal fauna of Australia. By comparing species richness patterns to null models, we show that species are distributed nonrandomly among genera. Using sister‐clade comparisons to control for clade age, we then find that faster diversification is significantly associated with larger geographical ranges and larger litters, but there is no evidence for an effect of body size or age at first breeding on diversification rates. We believe the most likely explanation for these patterns is that larger litters and geographical ranges increase diversification rates because they buffer species from extinction. We also discuss the possibility that positive effects of litter size and range size on diversification rates result from elevated speciation rates.     

Continental faunal exchange and the asymmetrical radiation of carnivores

Lineages arriving on islands may undergo explosive evolutionary radiations owing to the wealth of ecological opportunities. Although studies on insular taxa have improved our understanding of macroevolutionary phenomena, we know little about the macroevolutionary dynamics of continental exchanges. Here we study the evolution of eight Carnivora families that have migrated across the Northern Hemisphere to investigate if continental invasions also result in explosive diversification dynamics. We used a Bayesian approach to estimate speciation and extinction rates from a substantial dataset of fossil occurrences while accounting for the incompleteness of the fossil record. Our analyses revealed a strongly asymmetrical pattern in which North American lineages invading Eurasia underwent explosive radiations, whereas lineages invading North America maintained uniform diversification dynamics. These invasions into Eurasia were characterized by high rates of speciation and extinction. The radiation of the arriving lineages in Eurasia coincide with the decline of established lineages or phases of climate change, suggesting differences in the ecological settings between the continents may be responsible for the disparity in diversification dynamics. These results reveal long-term outcomes of biological invasions and show that the importance of explosive radiations in shaping diversity extends beyond insular systems and have significant impact at continental scales.     

Large-scale phylogenetic analyses reveal the causes of high tropical amphibian diversity

Many groups show higher species richness in tropical regions but the underlying causes remain unclear. Despite many competing hypotheses to explain latitudinal diversity gradients, only three processes can directly change species richness across regions: speciation, extinction and dispersal. These processes can be addressed most powerfully using large-scale phylogenetic approaches, but most previous studies have focused on small groups and recent time scales, or did not separate speciation and extinction rates. We investigate the origins of high tropical diversity in amphibians, applying new phylogenetic comparative methods to a tree of 2871 species. Our results show that high tropical diversity is explained by higher speciation in the tropics, higher extinction in temperate regions and limited dispersal out of the tropics compared with colonization of the tropics from temperate regions. These patterns are strongly associated with climate-related variables such as temperature, precipitation and ecosystem energy. Results from models of diversity dependence in speciation rate suggest that temperate clades may have lower carrying capacities and may be more saturated (closer to carrying capacity) than tropical clades. Furthermore, we estimate strikingly low tropical extinction rates over geological time scales, in stark contrast to the dramatic losses of diversity occurring in tropical regions presently.     

Investigating the evolution of floras: problems and progress — An introduction

The Cape flora of southern Africa is a remarkable hotspot for plant species diversity and endemism. At a meeting in Zurich in 2004 progress in understanding the evolution of this diversity was reviewed. In this symposium, four papers presenting several of the methods used in this investigation were reported. These papers deal with molecular dating methods, the reconstruction of ancestral habitats, with possible speciation scenarios for the Cape flora, and the importance of the correct sampling strategies.     

The origins of species richness in the Hymenoptera: insights from a family-level supertree

Background  

The order Hymenoptera (bees, ants, wasps, sawflies) contains about eight percent of all described species, but no analytical studies have addressed the origins of this richness at family-level or above. To investigate which major subtaxa experienced significant shifts in diversification, we assembled a family-level phylogeny of the Hymenoptera using supertree methods. We used sister-group species-richness comparisons to infer the phylogenetic position of shifts in diversification.     

Fossil biogeography: a new model to infer dispersal,extinction and sampling from palaeontological data

Methods in historical biogeography have revolutionized our ability to infer the evolution of ancestral geographical ranges from phylogenies of extant taxa, the rates of dispersals, and biotic connectivity among areas. However, extant taxa are likely to provide limited and potentially biased information about past biogeographic processes, due to extinction, asymmetrical dispersals and variable connectivity among areas. Fossil data hold considerable information about past distribution of lineages, but suffer from largely incomplete sampling. Here we present a new dispersal–extinction–sampling (DES) model, which estimates biogeographic parameters using fossil occurrences instead of phylogenetic trees. The model estimates dispersal and extinction rates while explicitly accounting for the incompleteness of the fossil record. Rates can vary between areas and through time, thus providing the opportunity to assess complex scenarios of biogeographic evolution. We implement the DES model in a Bayesian framework and demonstrate through simulations that it can accurately infer all the relevant parameters. We demonstrate the use of our model by analysing the Cenozoic fossil record of land plants and inferring dispersal and extinction rates across Eurasia and North America. Our results show that biogeographic range evolution is not a time-homogeneous process, as assumed in most phylogenetic analyses, but varies through time and between areas. In our empirical assessment, this is shown by the striking predominance of plant dispersals from Eurasia into North America during the Eocene climatic cooling, followed by a shift in the opposite direction, and finally, a balance in biotic interchange since the middle Miocene. We conclude by discussing the potential of fossil-based analyses to test biogeographic hypotheses and improve phylogenetic methods in historical biogeography.     

Generic species richness and body mass in North American mammals: Support for the inverse relationship of body size and speciation rate

Generic species richness, the number of species per genus, is examined as a function of mean generic body mass for extant North American mammals. Species richness decreases as an inverse power function with increased mass, and the Spearman rank correlation coefficient of the logio transformed data is significant (r_s= ‐0.37). When the data are partitioned by trophic level, the relationship is not statistically significant for carnivores but strengthens for herbivores (r_s= ‐0.46). This interesting but incidental effect is due to the negligible number of diminutive and excessively large carnivores, which is in turn determined by foraging strategies. Alternate hypotheses for the “right‐skewed”; size distribution of modern North American mammals, such as disproportionate extinction of large species, differential species longevity, and a geographical scaling function, are rejected in favor of the proposition that elevated levels of speciation are restricted to animals of small body mass, as originally proposed by Gould and Eldredge (1977). This phenomenon is explained as a function of habitat restriction and particularly in herbivores, limited home range size. Aquatic mammals, regardless of body size, speciate rarely. Cope's Rule, the tendency of many animal groups to evolve towards large size, is understood as a probabilistic statement reflecting the phylogenetic tendencies of a disproportionately high number of small species alive at any given point in time.     

Macroevolution of hoverflies (Diptera: Syrphidae): the effect of using higher‐level taxa in studies of biodiversity,and correlates of species richness

We test a near‐complete genus level phylogeny of hoverflies (Diptera: Syrphidae) for consistency with a null model of clade growth having uniform probabilities of speciation and extinction among contemporaneous species. The phylogeny is too unbalanced for this null model. Importantly, the degree of imbalance in the phylogeny depends on whether the phylogeny is analysed at the genus level or species level, suggesting that genera ought not to be used uncritically as surrogates for species in large‐scale evolutionary analyses. Tests for a range of morphological, life‐history and ecological correlates of diversity give equivocal results, but suggest that high species‐richness may be associated with sexual selection and diet breadth. We find no correlation between species‐richness and either body size or reproductive rate.     

From Mediterranean shores to central Saharan mountains: key phylogeographical insights from the genus Myrtus

Aim The Mediterranean region is often regarded as a crossroads where species of various origins meet. However, the biogeographical relationships between this region and contiguous Saharan, Macaronesian and Irano‐Turanian regions have not been investigated in detail. The aim of this study was to characterize the phylogeography of the circum‐Mediterranean species Myrtus communis and to investigate the origin of isolated central Saharan populations of Myrtus nivellei. Location The distribution ranges of M. communis from Macaronesia to the Irano‐Turanian region (173 sampled populations) and of M. nivellei in the mountains (Hoggar, Tassili n’Ajjer, Immidir, Tibesti) of the central Sahara (23 populations). Methods Nuclear ribosomal DNA (nrDNA) sequences of Myrtaceae were used to root the phylogeny of Myrtus, and to date its crown node, according to a detailed review of the palaeobotanical records used for multiple fossil calibration. Chloroplast DNA (cpDNA) sequences were analysed through the determination of genetic diversity indices and by statistical phylogeography. Results Both cpDNA and nrDNA markers indicated east–west genetic differentiation within M. communis. During the late Miocene, a key vicariance event affected the previous circum‐Mediterranean distribution of Myrtus, leading to the isolation of eastern populations. During the late Miocene or early Pliocene, two clades diverged: one is now scattered in the Mediterranean Basin and adjacent regions, whereas the other evolved in the western Mediterranean region. The differentiation of lineages during the Plio‐Pleistocene occurred mainly in the western part of the Mediterranean Basin, which has been at the origin of migrations towards Macaronesian islands and Saharan mountains. This is one of the first plant phylogeographical studies to report migrations from the Mediterranean to the Sahara. Main conclusions The genus Myrtus has persisted in the Mediterranean region since at least the Neogene and its biogeography reflects the cumulation of the species’ responses to successive palaeoenvironmental changes. The current distribution of the genus Myrtus in the Mediterranean Basin and in isolated areas, such as the Macaronesian islands and Saharan mountains, can be explained by the striking ability of this plant not only to persist locally in various refugia, but also to migrate.     

Supertree analyses of the roles of viviparity and habitat in the evolution of atherinomorph fishes

Using supertree phylogenetic reconstructions, we investigate how livebearing and freshwater adaptations may have shaped evolutionary patterns in the Atherinomorpha, a large clade (approximately 1500 extant species) of ray-finned fishes. Based on maximum parsimony reconstructions, livebearing appears to have evolved at least four times independently in this group, and no reversions to the ancestral state of oviparity were evident. With respect to habitat, at least five evolutionary transitions apparently occurred from freshwater to marine environments, at least two transitions in the opposite direction, and no clear ancestral state was identifiable. All viviparous clades exhibited more extant species than their oviparous sister taxa, suggesting that transitions to viviparity may be associated with cladogenetic diversification. Transitions to freshwater were usually, but not invariably associated with increased species richness, but the trend was, overall, not significant among sister clades. Additionally, we investigated whether livebearing and freshwater adaptations are currently associated with elevated risks of extinction as implied by species' presence on the 2004 IUCN Red List. Despite being correlated with decreased brood size, livebearing has not significantly increased extinction risk in the Atherinomorpha. However, freshwater species were significantly more likely than marine species to be listed as endangered.     

Dispersal ability and invasion success of Crepidula fornicata in a single gulf: insights from genetic markers and larval-dispersal model

The success of an exotic species relies on many factors including dispersal capabilities and adaptation to novel environments. In particular, rapid spread from an initial point of introduction favours long-term establishment of exotic species, especially when large genetic diversity is maintained during the colonization phase. We here focused on the slipper limpet, Crepidula fornicata, a species native to the western Atlantic that has successfully invaded European bays and estuaries since the end of the nineteenth century following repeated introductions. Its settlement at high densities has major consequences on the macro-benthic fauna and flora. The aim of the present study was to analyse the ability of C. fornicata for rapid diffusion and long-distance dispersal, at the level of a large French gulf, namely the gulf of St-Malo (covering 120 km in latitude and 40 km in longitude) in the English Channel. The genetic architecture of 16 populations distributed all over this gulf was investigated using five microsatellite loci. Genetic diversity was found to be high and did not vary significantly with population density, population age or geographic location. Moreover, despite potential isolation among populations due to a strong tidal regime and the action of wind-induced currents, only weak barriers to gene flow were found across the gulf. These results were in agreement with results obtained from a simple 2D larval dispersal model. Both genetic data and the simulation model highlighted the potential for rapid and efficient spread of C. fornicata at a regional level.     

A systematic and biogeographical study of epi- and hypogean populations of the Proasellus species group from Sardinia, central Italy and Jordan: allozyme insights

Genetic variation at 18 enzymatic loci was investigated in 10 epigean and three hypogean populations belonging to the Proasellus (Asellidae, Crustacea) species group, from Sardinia, central Italy, and Jordan, in order to clarify their systematics and evolutionary relationships. We found unexpectedly high levels of genetic divergence, which allowed us to recognize a number of genetically distinct species presently hidden under the name Proasellus coxalis . The group of Sardinian populations is the most genetically differentiated. Among the central Italian populations, the northernmost population is the earliest branch in the proposed phyletic scheme, whereas the remaining populations are genetically homogeneous and clustered as the sister taxon of the Sardinian populations. The Jordanian population is genetically differentiated versus both the central Italian and Sardinian groups. The evolutionary relationships seem to indicate that several waves of colonization by this genus occurred in Europe. The evolutionary times inferred from genetic distance data place the main splitting events at the end of the Miocene, in agreement with the paleogeography of the study areas.     

The ghosts of mammals past: biological and geographical patterns of global mammalian extinction across the Holocene

Although the recent historical period is usually treated as a temporal base-line for understanding patterns of mammal extinction, mammalian biodiversity loss has also taken place throughout the Late Quaternary. We explore the spatial, taxonomic and phylogenetic patterns of 241 mammal species extinctions known to have occurred during the Holocene up to the present day. To assess whether our understanding of mammalian threat processes has been affected by excluding these taxa, we incorporate extinct species data into analyses of the impact of body mass on extinction risk. We find that Holocene extinctions have been phylogenetically and spatially concentrated in specific taxa and geographical regions, which are often not congruent with those disproportionately at risk today. Large-bodied mammals have also been more extinction-prone in most geographical regions across the Holocene. Our data support the extinction filter hypothesis, whereby regional faunas from which susceptible species have already become extinct now appear less threatened; they may also suggest that different processes are responsible for driving past and present extinctions. We also find overall incompleteness and inter-regional biases in extinction data from the recent fossil record. Although direct use of fossil data in future projections of extinction risk is therefore not straightforward, insights into extinction processes from the Holocene record are still useful in understanding mammalian threat.     

Host‐associated genetic differentiation in a seed parasitic weevil Rhinusa antirrhini (Coleptera: Curculionidae) revealed by mitochondrial and nuclear sequence data

Plant feeding insects and the plants they feed upon represent an ecological association that is thought to be a key factor for the diversification of many plant feeding insects, through differential adaptation to different plant selective pressures. While a number of studies have investigated diversification of plant feeding insects above the species level, relatively less attention has been given to patterns of diversification within species, particularly those that also require plants for oviposition and subsequent larval development. In the case of plant feeding insects that also require plant tissues for the completion of their reproductive cycle through larval development, the divergent selective pressure not only acts on adults, but on the full life history of the insect. Here we focus attention on Rhinusa antirrhini (Curculionidae), a species of weevil broadly distributed across Europe that both feeds on, and oviposits and develops within, species of the plant genus Linaria (Plantaginaceae). Using a combination of mtDNA (COII) and nuclear DNA (EF1‐α) sequencing and copulation experiments we assess evidence for host associated genetic differentiation within R. antirrhini. We find substantial genetic variation within this species that is best explained by ecological specialisation on different host plant taxa. This genetic differentiation is most pronounced in the mtDNA marker, with patterns of genetic variation at the nuclear marker suggesting incomplete lineage sorting and/or gene flow between different host plant forms of R. antirrhini, whose origin is estimated to date to the mid‐Pliocene (3.77 Mya; 2.91–4.80 Mya).     

Timing of deep‐sea adaptation in dogfish sharks: insights from a supertree of extinct and extant taxa

Klug, S. & Kriwet, J. (2010). Timing of deep‐sea adaptation in dogfish sharks: insights from a supertree of extinct and extant taxa. —Zoologica Scripta, 39, 331–342. Dogfish sharks (Squaliformes) constitute a monophyletic group of predominantly deep‐water neoselachians, but the reasons and timing of their adaptation to this hostile environment remain ambiguous. Late Cretaceous dogfish sharks, which generally would be associated with deep‐water occur predominantly in shallow water environments. Did the end‐Cretaceous mass extinction event that eliminated large numbers of both terrestrial and aquatic taxa and clades including sharks trigger the evolutionary adaptation of present deep‐water dogfish sharks? Here, we construct, date, and analyse a genus‐level phylogeny of extinct and living dogfish sharks to bring a new perspective to this question. For this, eleven partial source trees of dogfish shark interrelationships were merged to create a comprehensive phylogenetic hypothesis. The resulting supertree is the most inclusive estimate of squaliform interrelationships that has been proposed to date containing 23 fossil and extant members of all major groups. ?Eoetmopterus represents the oldest dalatoid. ?Microetmopterus, ?Paraphorosoides, ?Proetmopterus and ?Squaliogaleus are stem‐group dalatoids in which bioluminescence most likely was not developed. According to our analyses, bioluminescence in dogfish sharks was already developed in the early Late Cretaceous indicating that these sharks adapted to deep‐water conditions most likely at about 100 Mya. The advantage of this reconstruction is that the fossil record is used directly for age node estimates rather than employing molecular clock approaches.     

Fire ant predation on native and introduced subterranean termites in the laboratory: effect of high soldier number in Coptotermes formosanus

Abstract.

• 1 Native Reticulitermes spp. Holmgren and the introduced Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) were exposed to predation in the laboratory by Solenopsis invicta Buren (Hymenoptera: Formicidae), a known predator of Reticulitermes.
• 2 In one experiment, both taxa contained the 2.4% soldiers commonly found in Reticulitermes. In a second experiment, Reticulitermes contained 2.4% and C.formosanus a more normal 18.3% soldiers.
• 3 When soldier proportions were equal, C.formosanus soldiers suffered less of a decrease in survivorship due to predation compared with Reticulitermes soldiers. Little difference was found between taxa in the effect of predation on termite workers or in the effect of termites on predator survivorship.
• 4 When soldier proportions were unequal, both C.formosanus castes suffered less from predation than those of Reticulitermes. Again, little difference was found in the effect of termites on ants.
• 5 C.formosanus showed less movement into new containers when soldier number was abnormally low, compared with both taxa with normal caste proportions.