Bee pollination services and the burden of biogeography.

Native bees augment pollination services in the Northern Hemisphere, especially cultivated apple crops, yet Southern Hemisphere contexts are poorly known. We observed the foraging behaviour of 69 354 invertebrate flower visitors in Australian orchards (two regions, 3 years) to assess the efficacy of pollination service (Peff). Native stingless bees and introduced honey bees were the most abundant visitors and most efficacious pollinators (Tetragonula Peff = 6.16; Apis Peff = 13.02), with Tetragonula becoming important service providers above 22°C. However, visits by tree-nesting stingless bees decreased with distance from native forest (less than 200 m) and their tropical/subtropical distribution precludes pollination service in other major Australian apple-producing regions. More broadly distributed native allodapine and halictine bees transferred the most pollen per-visit, but their low abundances reduce efficacies (Exoneura Peff = 0.03; Lasioglossum Peff = 0.06), resulting in a general dependence on honey bees. This reliance is a burden of biogeography, since key Northern Hemisphere pollinators of apple (Andrena, Apis, Bombus, Osmia) do not naturally occur in Australasia-where there is only 15% generic overlap with Central Asian bees sympatric with wild apple distributions (cf. Palaearctic 66% and Nearctic 46% generic overlaps). The historical biogeography of bees therefore drives an extreme dependence on one introduced species for apple pollination in Australia.

The final frontier: ecological and evolutionary dynamics of a global parasite invasion.

Studying rapid biological changes accompanying the introduction of alien organisms into native ecosystems can provide insights into fundamental ecological and evolutionary theory. While powerful, this quasi-experimental approach is difficult to implement because the timing of invasions and their consequences are hard to predict, meaning that baseline pre-invasion data are often missing. Exceptionally, the eventual arrival of Varroa destructor (hereafter Varroa) in Australia has been predicted for decades. Varroa is a major driver of honeybee declines worldwide, particularly as vectors of diverse RNA viruses. The detection of Varroa in 2022 at over a hundred sites poses a risk of further spread across the continent. At the same time, careful study of Varroa's spread, if it does become established, can provide a wealth of information that can fill knowledge gaps about its effects worldwide. This includes how Varroa affects honeybee populations and pollination. Even more generally, Varroa invasion can serve as a model for evolution, virology and ecological interactions between the parasite, the host and other organisms.

Differential transcriptomic responses to heat stress in surface and subterranean diving beetles.

Subterranean habitats are generally very stable environments, and as such evolutionary transitions of organisms from surface to subterranean lifestyles may cause considerable shifts in physiology, particularly with respect to thermal tolerance. In this study we compared responses to heat shock at the molecular level in a geographically widespread, surface-dwelling water beetle to a congeneric subterranean species restricted to a single aquifer (Dytiscidae: Hydroporinae). The obligate subterranean beetle Paroster macrosturtensis is known to have a lower thermal tolerance compared to surface lineages (CTmax 38 °C cf. 42-46 °C), but the genetic basis of this physiological difference has not been characterized. We experimentally manipulated the thermal environment of 24 individuals to demonstrate that both species can mount a heat shock response at high temperatures (35 °C), as determined by comparative transcriptomics. However, genes involved in these responses differ between species and a far greater number were differentially expressed in the surface taxon, suggesting it can mount a more robust heat shock response; these data may underpin its higher thermal tolerance compared to subterranean relatives. In contrast, the subterranean species examined not only differentially expressed fewer genes in response to increasing temperatures, but also in the presence of the experimental setup employed here alone. Our results suggest P. macrosturtensis may be comparatively poorly equipped to respond to both thermally induced stress and environmental disturbances more broadly. The molecular findings presented here have conservation implications for P. macrosturtensis and contribute to a growing narrative concerning weakened thermal tolerances in obligate subterranean organisms at the molecular level.

Parallel decay of vision genes in subterranean water beetles.

In the framework of neutral theory of molecular evolution, genes specific to the development and function of eyes in subterranean animals living in permanent darkness are expected to evolve by relaxed selection, ultimately becoming pseudogenes. However, definitive empirical evidence for the role of neutral processes in the loss of vision over evolutionary time remains controversial. In previous studies, we characterized an assemblage of independently-evolved water beetle (Dytiscidae) species from a subterranean archipelago in Western Australia, where parallel vision and eye loss have occurred. Using a combination of transcriptomics and exon capture, we present evidence of parallel coding sequence decay, resulting from the accumulation of frameshift mutations and premature stop codons, in eight phototransduction genes (arrestins, opsins, ninaC and transient receptor potential channel genes) in 32 subterranean species in contrast to surface species, where these genes have open reading frames. Our results provide strong evidence to support neutral evolutionary processes as a major contributing factor to the loss of phototransduction genes in subterranean animals, with the ultimate fate being the irreversible loss of a light detection system.

Does effective population size affect rates of molecular evolution: Mitochondrial data for host/parasite species pairs in bees suggests not.

Adaptive evolutionary theory argues that organisms with larger effective population size (N e) should have higher rates of adaptive evolution and therefore greater capacity to win evolutionary arm races. However, in some certain cases, species with much smaller N e may be able to survive besides their opponents for an extensive evolutionary time. Neutral theory predicts that accelerated rates of molecular evolution in organisms with exceedingly small N e are due to the effects of genetic drift and fixation of slightly deleterious mutations. We test this prediction in two obligate social parasite species and their respective host species from the bee tribe Allodapini. The parasites (genus Inquilina) have been locked into tight coevolutionary arm races with their exclusive hosts (genus Exoneura) for ~15 million years, even though Inquilina exhibit N e that are an order of magnitude smaller than their host. In this study, we compared rates of molecular evolution between host and parasite using nonsynonymous to synonymous substitution rate ratios (dN/dS) of eleven mitochondrial protein-coding genes sequenced from transcriptomes. Tests of selection on mitochondrial genes indicated no significant differences between host and parasite dN/dS, with evidence for purifying selection acting on all mitochondrial genes of host and parasite species. Several potential factors which could weaken the inverse relationship between N e and rate of molecular evolution are discussed.

Development and evaluation of a custom bait design based on 469 single-copy protein-coding genes for exon capture of isopods (Philosciidae: Haloniscus).

Transcriptome-based exon capture approaches, along with next-generation sequencing, are allowing for the rapid and cost-effective production of extensive and informative phylogenomic datasets from non-model organisms for phylogenetics and population genetics research. These approaches generally employ a reference genome to infer the intron-exon structure of targeted loci and preferentially select longer exons. However, in the absence of an existing and well-annotated genome, we applied this exon capture method directly, without initially identifying intron-exon boundaries for bait design, to a group of highly diverse Haloniscus (Philosciidae), paraplatyarthrid and armadillid isopods, and examined the performance of our methods and bait design for phylogenetic inference. Here, we identified an isopod-specific set of single-copy protein-coding loci, and a custom bait design to capture targeted regions from 469 genes, and analysed the resulting sequence data with a mapping approach and newly-created post-processing scripts. We effectively recovered a large and informative dataset comprising both short (<100 bp) and longer (>300 bp) exons, with high uniformity in sequencing depth. We were also able to successfully capture exon data from up to 16-year-old museum specimens along with more distantly related outgroup taxa, and efficiently pool multiple samples prior to capture. Our well-resolved phylogenies highlight the overall utility of this methodological approach and custom bait design, which offer enormous potential for application to future isopod, as well as broader crustacean, molecular studies.

Evidence for speciation underground in diving beetles (Dytiscidae) from a subterranean archipelago.

Most subterranean animals are assumed to have evolved from surface ancestors following colonization of a cave system; however, very few studies have raised the possibility of "subterranean speciation" in underground habitats (i.e., obligate cave-dwelling organisms [troglobionts] descended from troglobiotic ancestors). Numerous endemic subterranean diving beetle species from spatially discrete calcrete aquifers in Western Australia (stygobionts) have evolved independently from surface ancestors; however, several cases of sympatric sister species raise the possibility of subterranean speciation. We tested this hypothesis using vision (phototransduction) genes that are evolving under neutral processes in subterranean species and purifying selection in surface species. Using sequence data from 32 subterranean and five surface species in the genus Paroster (Dytiscidae), we identified deleterious mutations in long wavelength opsin (lwop), arrestin 1 (arr1), and arrestin 2 (arr2) shared by a sympatric sister-species triplet, arr1 shared by a sympatric sister-species pair, and lwop and arr2 shared among closely related species in adjacent calcrete aquifers. In all cases, a common ancestor possessed the function-altering mutations, implying they were already adapted to aphotic environments. Our study represents one of the first confirmed cases of subterranean speciation in cave insects. The assessment of genes undergoing pseudogenization provides a novel way of testing modes of speciation and the history of diversification in blind cave animals.

Massive Parallel Regression: A Précis of Genetic Mechanisms for Vision Loss in Diving Beetles.

Two tribes of subterranean dytiscid diving beetles independently colonized groundwater systems of the Western Australian arid zone, a habitat transition that was most likely driven by the contraction of surface water bodies following late Neogene aridification of the Australian continent. These "stygofauna" are now trapped within discrete calcrete aquifers that have formed in paleodrainage valleys, resulting in the world's most diverse radiations of subterranean dytiscid beetles. Approximately 100 species from three genera exhibit partial or fully regressed visual systems and are essentially blind. This unique study system, with multiple independent transitions to subterranean life enables regressive and adaptive evolutionary processes to be studied in parallel at an unheralded comparative scale. Here we provide an overview of the progression of dytiscid beetle research and undertake a literature survey of published research within the field of regressive evolution as it applies to eye loss. We detail our exploration of insect vision genes for signatures of adaptive and neutral evolutionary mechanisms related to eye regression, largely within photoreceptor and eye pigment genes. Our project makes use of transcriptome data from five representative dytiscid beetle species (two surface and three subterranean) in order to design a customized set of RNA baits for use in a hybrid-capture method to target a pool of vision genes sequenced using high-throughput Illumina platforms. This methodological design permits the assessment of modifications in the genomic sequence of beetle vision genes at a much broader scale than Sanger sequencing, enabling a higher number of both target species and genes to be simultaneously assessed relative to research time-investments. Based on our literature search criteria of the research field ("regressive evolution" + "eyes"), 81 papers have been published since the late 1980s accruing an h-index of 27 and a mean citation rate of 24.57. Collective annual citations for this field of research have surged over the past 5 years, an indication that broader scientific community interest is gaining momentum. The majority of publications (75%) have focused on the chordate clade Actinopterygii. Historically, research on variant subterranean taxa has faced difficulties inferring the evolutionary mechanisms of eye regression (and vision loss) using molecular approaches because only a handful of target genes could be feasibly addressed within grant funding cycles. From a comparative phylogenetic perspective, next-generation sequencing approaches applied to stygobiontic dytiscid beetles hold the potential to greatly improve our understanding of the genetic mechanisms underlying regressive evolution generally.

A revised phylogeny of macropathine cave crickets (Orthoptera: Rhaphidophoridae) uncovers a paraphyletic Australian fauna.

Australian cave crickets are members of the subfamily Macropathinae (Orthoptera: Rhaphidophoridae). The subfamily is thought to have originated prior to the tectonic separation of the supercontinent Gondwana based on distributions of extant lineages and molecular phylogenetic evidence, although the Australian fauna have been underrepresented in previous studies. The current study augments existing multigene data (using 12S, 16S, and 28S rRNA genes) to investigate the placement of the Australian representatives within the Macropathinae and to assess divergence dates of select clades. Results suggest that the endemic Tasmanian genus Parvotettix is the sister lineage to the remaining members of the subfamily, an outcome that presents a paraphyletic Australian fauna in contrast to previous studies. All other Australian taxa represented in this study (Micropathus and Novotettix) emerged as a sister group to the New Zealand and South American macropathine lineages. Estimation of phylogenetic divergence ages among the aforementioned clades were calibrated using two methods, in absence of suitable fossil records: (i) tectonic events depicting the fragmentation of Gondwanan landmasses that invoke vicariant scenarios of present day geographic distributions; and (ii) molecular evolutionary rates. Geological calibrations place the median age of the most recent common ancestor of extant macropathines at ∼125 to ∼165 Ma, whereas analyses derived from molecular substitution rates suggest a considerably younger origin of ∼32 Ma. This phylogenetic study represents the most rigorous taxonomic sampling of the Australian cave cricket fauna to date and stresses the influence of lineage representation on biogeographic inference.

Opsin transcripts of predatory diving beetles: a comparison of surface and subterranean photic niches.

The regressive evolution of eyes has long intrigued biologists yet the genetic underpinnings remain opaque. A system of discrete aquifers in arid Australia provides a powerful comparative means to explore trait regression at the genomic level. Multiple surface ancestors from two tribes of diving beetles (Dytiscidae) repeatedly invaded these calcrete aquifers and convergently evolved eye-less phenotypes. We use this system to assess transcription of opsin photoreceptor genes among the transcriptomes of two surface and three subterranean dytiscid species and test whether these genes have evolved under neutral predictions. Transcripts for UV, long-wavelength and ciliary-type opsins were identified from the surface beetle transcriptomes. Two subterranean beetles showed parallel loss of all opsin transcription, as expected under 'neutral' regressive evolution. The third species Limbodessus palmulaoides retained transcription of a long-wavelength opsin (lwop) orthologue, albeit in an aphotic environment. Tests of selection on lwop indicated no significant differences between transcripts derived from surface and subterranean habitats, with strong evidence for purifying selection acting on L. palmulaoides lwop. Retention of sequence integrity and the lack of evidence for neutral evolution raise the question of whether we have identified a novel pleiotropic role for lwop, or an incipient phase of pseudogene development.

Photic niche invasions: phylogenetic history of the dim-light foraging augochlorine bees (Halictidae).

Most bees rely on flowering plants and hence are diurnal foragers. From this ancestral state, dim-light foraging in bees requires significant adaptations to a new photic environment. We used DNA sequences to evaluate the phylogenetic history of the most diverse clade of Apoidea that is adapted to dim-light environments (Augochlorini: Megalopta, Megaloptidia and Megommation). The most speciose lineage, Megalopta, is distal to the remaining dim-light genera, and its closest diurnal relative (Xenochlora) is recovered as a lineage that has secondarily reverted to diurnal foraging. Tests for adaptive protein evolution indicate that long-wavelength opsin shows strong evidence of stabilizing selection, with no more than five codons (2%) under positive selection, depending on analytical procedure. In the branch leading to Megalopta, the amino acid of the single positively selected codon is conserved among ancestral Halictidae examined, and is homologous to codons known to influence molecular structure at the chromophore-binding pocket. Theoretically, such mutations can shift photopigment λ(max) sensitivity and enable visual transduction in alternate photic environments. Results are discussed in light of the available evidence on photopigment structure, morphological specialization and biogeographic distributions over geological time.

The evolution of eusociality in allodapine bees: workers began by waiting.

Understanding how sterile worker castes in social insects first evolved is one of the supreme puzzles in social evolution. Here, we show that in the bee tribe Allodapini, the earliest societies did not entail a foraging worker caste, but instead comprised females sharing a nest with supersedure of dominance. Subordinates delayed foraging until they became reproductively active, whereupon they provided food for their own brood as well as for those of previously dominant females. The earliest allodapine societies are, therefore, not consistent with an 'evo-devo' paradigm, where decoupling of foraging and reproductive tasks is proposed as a key early step in social evolution. Important features of these ancestral societies were insurance benefits for dominants, headstart benefits for subordinates and direct reproduction for both. The two lineages where morphologically distinct foraging worker castes evolved both occur in ecosystems with severe constraints on independent nesting and where brood rearing periods are very seasonally restricted. These conditions would have strongly curtailed dispersal options and increased the likelihood that dominance supersedure occurred after brood rearing opportunities were largely degraded. The origins of foraging castes, therefore, represented a shift towards assured fitness gains by subordinates, mediated by the dual constraints of social hierarchies and environmental harshness.

Nest descriptions of Megalopta aegis (Vachal) and M. guimaraesi Santos & Silveira (Hymenoptera, Halictidae) from the Brazilian Cerrado / Descrição dos ninhos de Megalopta aegis (Vachal) e M. guimaraesi Santos & Silveira (Hymenoptera, Halictidae) do Cerrado

We present the first data on the nesting biology of Megalopta aegis and M. guimaraesi from southeastern Brazil. Nests were collected in the Área de Proteção Ambiental Água Limpa, Bauru, São Paulo state. Our data suggest that nest architecture is conserved throughout all species of Megalopta. Two nests of M. guimaraesi consisted of a single female with brood. Of three M. aegis nests, two contained single females with brood and the third nest contained three adult females, with three times more brood than any single female nest. This observation suggests that social behavior in M. aegis is facultative, as known for other Megalopta species.

Apresentamos os primeiros registros da biologia de nidificação de Megalopta aegis (Vachal) e de M. guimaraesi Santos & Silveira, do sudeste do Brasil. Os ninhos foram coletados na Área de Proteção Ambiental Água Limpa, Bauru, estado de São Paulo. Os dados sugerem que a arquitetura do ninho em Megalopta seja conservada entre suas espécies. Dois ninhos de M. guimaraesi continham apenas uma única fêmea com imaturos. Dos três ninhos de M. aegis, dois possuíam uma única fêmea com imaturos e o terceiro ninho continha três fêmeas adultas com três vezes mais imaturos do que nos ninhos com apenas uma fêmea. Essa observação sugere que o comportamento social em M. aegis seja facultativo, semelhante a outras espécies de Megalopta.

Behavioural environments and niche construction: the evolution of dim-light foraging in bees.

Most bees forage for floral resources during the day, but temporal patterns of foraging activity vary extensively, and foraging in dim-light environments has evolved repeatedly. Facultative dim-light foraging behaviour is known in five of nine families of bees, while obligate behaviour is known in four families and evolved independently at least 19 times. The light intensity under which bees forage varies by a factor of 10(8), and therefore the evolution of dim-light foraging represents the invasion of a new, extreme niche. The repeated evolution of dim-light foraging behaviour in bees allows tests of the hypothesis that behaviour acts as an evolutionary pacemaker. With the exception of one species of Apis, facultative dim-light foragers show no external structural traits that are thought to enable visually mediated flight behaviour in low-light environments. By contrast, most obligate dim-light foragers show a suite of convergent optical traits such as enlarged ocelli and compound eyes. In one intensively studied species (Megalopta genalis) these optical changes are associated with neurobiological changes to enhance photon capture. The available ecological evidence suggests that an escape from competition for pollen and nectar resources and avoidance of natural enemies are driving factors in the evolution of obligate dim-light foraging.

Social complexity in bees is not sufficient to explain lack of reversions to solitary living over long time scales.

BACKGROUND: The major lineages of eusocial insects, the ants, termites, stingless bees, honeybees and vespid wasps, all have ancient origins (> or = 65 mya) with no reversions to solitary behaviour. This has prompted the notion of a 'point of no return' whereby the evolutionary elaboration and integration of behavioural, genetic and morphological traits over a very long period of time leads to a situation where reversion to solitary living is no longer an evolutionary option. RESULTS: We show that in another group of social insects, the allodapine bees, there was a single origin of sociality > 40 mya. We also provide data on the biology of a key allodapine species, Halterapis nigrinervis, showing that it is truly social. H. nigrinervis was thought to be the only allodapine that was not social, and our findings therefore indicate that there have been no losses of sociality among extant allodapine clades. Allodapine colony sizes rarely exceed 10 females per nest and all females in virtually all species are capable of nesting and reproducing independently, so these bees clearly do not fit the 'point of no return' concept. CONCLUSION: We argue that allodapine sociality has been maintained by ecological constraints and the benefits of alloparental care, as opposed to behavioural, genetic or morphological constraints to independent living. Allodapine brood are highly vulnerable to predation because they are progressively reared in an open nest (not in sealed brood cells), which provides potentially large benefits for alloparental care and incentives for reproductives to tolerate potential alloparents. We argue that similar vulnerabilities may also help explain the lack of reversions to solitary living in other taxa with ancient social origins.

Origins of social parasitism: the importance of divergence ages in phylogenetic studies.

Phylogenetic studies on insect social parasites have found very close host-parasite relationships, and these have often been interpreted as providing evidence for sympatric speciation. However, such phylogenetic inferences are problematic because events occurring after the origin of parasitism, such as extinction, host switching and subsequent speciation, or an incomplete sampling of taxa, could all confound the interpretation of phylogenetic relationships. Using a tribe of bees where social parasitism has repeatedly evolved over a wide time-scale, we show the problems associated with phylogenetic inference of sympatric speciation. Host-parasite relationships of more ancient species appear to support sympatric speciation, whereas in a case where parasitism has evolved very recently, sympatric speciation can be ruled out. However, in this latter case, a single extinction event would have lead to relationships that support sympatric speciation, indicating the importance of considering divergence ages when analysing the modes of social parasite evolution.

Molecular phylogenetics of the exoneurine allodapine bees reveal an ancient and puzzling dispersal from Africa to Australia.

Previous phylogenetic studies of the bee tribe Allodapini suggested a puzzling biogeographic problem: one of the key basal divergences involved separation of the southern African and southern Australian clades at a very early stage in allodapine evolution, but no taxa occur in the Palaearctic or Asian regions that might suggest a Laurasian dispersal route. However, these studies lacked sufficient sequence data and appropriate maximum likelihood partition models to provide reliable phylogenetic estimates and enable alternative biogeographic hypotheses to be distinguished. Using Bayesian and penalized likelihood approaches and an expanded sequence and taxon set we examine phylogenetic relationships between the Australian, African, and Malagasy groups and estimate divergence times for key nodes. We show that divergence of the three basal Australian clades (known as the exoneurines) occurred at least 25 Mya following a single colonization event, and that this group diverged from the African + Madagascan clade at least 30 Mya, but actual divergence dates are likely to be much older than these very conservative limits. The bifurcation order of the exoneurine clades was not resolved and analyses could not rule out the existence of a hard polytomy, suggesting rapid radiation after colonization of Australia. Their divergence involved major transitions in life history traits and these placed constraints on the kinds of social organization that subsequently evolved in each lineage. Early divergence between the African, Malagasy, and Australian clades presents a major puzzle for historical biogeography: node ages are too recent for Gondwanan vicariance hypotheses, but too early for Laurasian dispersal scenarios. We suggest a scenario involving island hopping across the Indian Ocean via a series of now largely submerged elements of the Kergulen Plateau and Broken Ridge provinces, both of which are known to have had subaerial formations during the Cenozoic. [Bayesian; biogeography; dispersal; Gondwana; Kerguelen Plateau; penalized likelihood.].

Molecular phylogenetics of the allodapine bee genus Braunsapis: A-T bias and heterogeneous substitution parameters.

Extreme AT bias in Hymenopteran mitochondrial genes have created difficulties for molecular phylogenetic analyses, especially for older divergences where multiple substitutions can erode signal. Heterogeneity in the evolutionary rates of different codon positions and different genes also appears to have been a major problem in resolving ancient divergences in allodapine bees. Here we examine the phylogeny of relatively recent divergences in the allodapine bee genus Braunsapis. We examined heterogeneity in nucleotide substitution parameters for one nuclear gene and codon positions in two mitochondrial genes, exploring various phylogenetic analyses for recovering relationships among species from Africa, Madagascar, southern Asia, and Australia. We explored maximum parsimony, maximum likelihood, Log determinant and Bayesian analyses. Broad topological features of best fit trees tended to be similar for equivalent data sets (e.g., total, or with 3rd mt positions excluded), regardless of the analytic method used (e.g., maximum likelihood or Bayesian). Analyses that used the total data set without modelling partitions separately gave unlikely results, indicating that the Malagasy species was most closely related to Australian species. However, analyses that excluded 3rd mitochondrial positions, or modelled partitions separately, suggested that the Malagasy species falls within the African clade. The unlikely topologies apparently result from long branch attraction, and this problem is ameliorated where modelling allows more realistic estimates of base composition and evolutionary rates for 3rd mitochondrial positions. However, we found that even when codon positions are modelled separately, estimated evolutionary rates for 3rd mitochondrial positions are likely to underestimate true rates. Long branch attraction and multiple substitutions are likely to be much more difficult to circumvent in analyses that explore older, generic-level, divergences in allodapine bees where overwriting is expected to be much more extreme. Our results indicate an African origin for Braunsapis, followed by a single, very early, dispersal event into Asia and then by a later dispersal event into Australia. The Malagasy species is derived from within the African clade.