Large Taxonomic Groups Research Articles

Level of environmental threat posed by horticultural trade in Cactaceae.

Ornamental horticulture has been identified as an important threat to plant biodiversity and is a major pathway for plant invasions worldwide. In this context, the family Cactaceae is particularly challenging because it is considered the fifth most threatened large taxonomic group in the world; several species are among the most widespread and damaging invasive species; and Cactaceae is one of the most popular horticultural plant groups. Based on the Convention on International Trade in Endangered Species of Wild Flora and Fauna and the 11 largest online auction sites selling cacti, we documented the international cactus trade. To provide an in-depth look at the dynamics of the industry, we surveyed the businesses involved in the cactus trade in South Africa (a hotspot of cactus trade and invasions). We purchased seeds of every available species and used DNA barcoding to identify species to the genus level. Although <20% of this trade involved threatened species and <3% involved known invasive species, many species were identified by a common name. However, only 0.02% of the globally traded cacti were collected from wild populations. Despite a large commercial network, all South African imports (of which 15% and 1.5% were of species listed as threatened and invasive, respectively) came from the same source. With DNA barcoding, we identified 24% of the species to genus level. Based on our results, we believe that if trade restrictions are placed on the small proportion of cacti that are invasive and there is no major increase in harvesting of native populations, then the commercial trade in cactus poses a negligible environmental threat. However, there are currently no effective methods for easily identifying which cacti are traded, and both the illicit harvesting of cacti from the wild and the informal trade in invasive taxa pose on-going conservation challenges.

Distribution of the tryptophan pathway-derived defensive secondary metabolites gramine and benzoxazinones in Poaceae.

The Poaceae is a large taxonomic group consisting of approximately 12,000 species and is classified into 12 subfamilies. Gramine and benzoxazinones (Bxs), which are biosynthesized from the tryptophan pathway, are well-known defensive secondary metabolites in the Poaceae. We analyzed the presence or absence of garamine and Bxs in 64 species in the Poaceae by LC-MS/MS. We found that Hordeum brachyantherum and Hakonechloa macra accumulated gramine, but the presence of gramine was limited to small groups of species. We also detected Bxs in four species in the Pooideae and six species in the Panicoideae. In particular, four species in the Paniceae tribe in Panicoideae accumulaed Bxs, indicating that this tribe is a center of the Bx distribution. Bxs were absent in the subfamilies other than Pooideae and Panicoideae. These findings provide an overview of biased distribution of gramine and Bxs in Poaceae species.

The general dynamic model of island biogeography revisited at the level of major flowering plant families

AbstractAimThe general dynamic model (GDM) proposed by Whittaker et al. () has become a widely accepted theoretical framework in island biogeography. In this study, we explore whether GDM predictions hold when overall plant diversity is deconstructed into major plant families.Location101 islands from 14 oceanic archipelagos world‐wide.MethodsOccurrence data for all species of nine large, cosmopolitan flowering plant families were used to test predictions derived from the GDM. We analysed the effects of island area and age on species richness as well as number and percentage of single‐island endemic species per family using mixed‐effect models.ResultsTotal species and endemic richness as well as the percentage of endemic species showed the predicted hump‐shaped relationship with island age. The overall pattern was mainly driven by few species‐rich plant families. Varying patterns were found for individual families, some of them opposing the general trend. In most cases, native and endemic species richness peaked much earlier in the island life cycle than suggested by the GDM. The contribution of area to the explained variation of all dependent variables was much higher than that of island age.Main conclusionsThe results suggest that biodiversity‐age relationships reported for large taxonomic groups like plants are driven by only a few species‐rich clades. The way these families influence the overall patterns of species richness and endemism is related to family‐specific properties, such as evolutionary history or dispersal strategies. Deviances from the GDM predictions can hence largely be explained by family characteristics and considering taxon‐specific traits may help to further improve the explanatory power of the GDM. Families not following the expectations, like Orchidaceae, may be particularly valuable candidates to unveil so far neglected drivers of island biogeographical patterns.

Targeted sequencing for high-resolution evolutionary analyses following genome duplication in salmonid fish: Proof of concept for key components of the insulin-like growth factor axis

High-throughput sequencing has revolutionised comparative and evolutionary genome biology. It has now become relatively commonplace to generate multiple genomes and/or transcriptomes to characterize the evolution of large taxonomic groups of interest. Nevertheless, such efforts may be unsuited to some research questions or remain beyond the scope of some research groups. Here we show that targeted high-throughput sequencing offers a viable alternative to study genome evolution across a vertebrate family of great scientific interest. Specifically, we exploited sequence capture and Illumina sequencing to characterize the evolution of key components from the insulin-like growth (IGF) signalling axis of salmonid fish at unprecedented phylogenetic resolution. The IGF axis represents a central governor of vertebrate growth and its core components were expanded by whole genome duplication in the salmonid ancestor ~95Ma. Using RNA baits synthesised to genes encoding the complete family of IGF binding proteins (IGFBP) and an IGF hormone (IGF2), we captured, sequenced and assembled orthologous and paralogous exons from species representing all ten salmonid genera. This approach generated 299 novel sequences, most as complete or near-complete protein-coding sequences. Phylogenetic analyses confirmed congruent evolutionary histories for all nineteen recognized salmonid IGFBP family members and identified novel salmonid-specific IGF2 paralogues. Moreover, we reconstructed the evolution of duplicated IGF axis paralogues across a replete salmonid phylogeny, revealing complex historic selection regimes - both ancestral to salmonids and lineage-restricted - that frequently involved asymmetric paralogue divergence under positive and/or relaxed purifying selection. Our findings add to an emerging literature highlighting diverse applications for targeted sequencing in comparative-evolutionary genomics. We also set out a viable approach to obtain large sets of nuclear genes for any member of the salmonid family, which should enable insights into the evolutionary role of whole genome duplication before additional nuclear genome sequences become available.

Wood Anatomy of Brassicales: New Information, New Evolutionary Concepts

Wood anatomical data for the 19 families of Brassicales are presented, based on light microscopy and scanning electron microscopy (SEM), arranged according to recent molecular phylogenetic evidence. Because of large species numbers and diversity in ecology and growth form, Brassicales are an ideal case study group for understanding wood evolution. Features newly reported include vestured pits in Cleomaceae, Koeberliniaceae, Pentadiplandraceae, Salvadoraceae, and Setchellanthaceae. Vesturing of primary xylem helices is shown for Raphanus (first report in angiosperms). Fiber dimorphism is newly reported in some genera of the crown group (Capparaceae + Cleomaceae + Brassicaceae). The fiber-tracheid is probably the ancestral imperforate tracheary element type for Brassicales, and from it, libriform fibers, living fibers (including septate fibers), and tracheids have likely been derived. The Baileyan concept of unidirectional evolution from tracheids to libriform fibers must have many exceptions in angiosperms, and tracheids are not uniform. Tracheids occur in Emblingiaceae, Koeberliniaceae, Pentadiplandraceae, Stixaceae, and Tropaeolaceae. Synapomorphies can be identified, as in the Akaniaceae—Tropaeolaceae clade (rays of two sizes, living fibers, scalariform perforation remnants) and the Moringaceae-Caricaceae clade (ground tissue of wood composed of thin-walled fibers or similar parenchymatous cells). Wood of Brassicales is mostly not paedomorphic, although paedomorphic characters suggesting secondary woodiness occur within the families Brassicaceae (abundance of upright ray cells, raylessness), Caricaceae, Cleomaceae, and Moringaceae. Brassicales are probably ancestrally woody, and wood of Sapindales and Malvales has a number of key character states (plesiomorphies) like those in Brassicales, as would be predicted by current molecular phylogenies. Surveys of large taxonomic groupings, such as Brassicales, tend to yield more examples of homoplasies and apomorphies that can be interpreted in terms of adaptation and functional interlinkage (e.g., ray evolution paralleling imperforate tracheary element evolution). In turn, these features can be interpreted in terms of ecology (e.g., xeric habitats) and growth forms (e.g., tree succulents). The assemblages of wood character information in a reasonably well known order of angiosperms permits hypotheses about wood evolution in angiosperms as a whole. Some of the more important hypotheses presented include: (1), that evolution of wood (and other) characters is always progressive, with gene overlays (silencing, modification, etc.) and simultaneous changes in multiple features, so that ancestral conditions are never truly re-attained. (2). Not all characters are of equal value in water economy of any given plant; some (presence of tracheids) may supersede others, and xeromorphic characters can be arranged relative to each other in tiers, although various taxonomic groups have different rosters of conductive safety features. (3). Heterochrony (protracted juvenilism, accelerated adulthood) is extensively represented in angiosperms, and acts as an overlay that is a source of diversity that angiosperms have drawn on since their inception (probably as minimally woody plants). (4). There may be no “purely taxonomic” characters, because genes of an organism relate primarily to changes, ancient and new, that are of adaptive significance, although we may not be able to detect selective value, past or present. Although many families of Brassicales are small and represent occupancy of specialized or extreme habitats (Batis, Koeberlinia, Moringa), active speciation in Brassicaceae and Capparaceae is related to tolerance of drought and cold with mechanisms such as vestured pits, narrow vessels, and abbreviation in life cycle length.

Optimisation of Conditions for Extraction of Biologically Active Compounds from Common Bryophytes in Latvia / Latvijâ Augoðu Briofîtu Ekstrakcijas Apstâkïu Optimizâcijas Ietekme Uz Bioloìiski Aktîviem Sekundârajiem Metabolîtiem

Abstract Bryophytes are the second largest taxonomic group in the plant kingdom. They contain a high number of biologically active compounds. Studies of their composition are important for understanding evolutionary processes in the plant kingdom. The aim of this study was to assess bryophyte secondary metabolite extraction options and to increase the yields of polyphenols and substances determining the free radical scavenging activity of bryophyte extracts. Similar studies have been conducted using higher plants as model organisms, but not using bryophytes. Comparison of five extraction methods (conventional, Soxhlet extraction, treatment with microwaves, ultrasound, and supercritical CO2 extraction) and several solvents with differing polarity showed microwave-assisted extraction as the most promising approach to obtain highest yields of extractives. The main factors that contributed to the efficiency of extraction were type of solvent, temperature, and the solvent to bryophyte mass ratio. The extracts obtained from bryophytes had remarkable antioxidant activity, the extent of which depended on the extraction conditions and bryophyte species. The extraction conditions can be optimised, and the total polyphenol content can be increased by up to 50% in comparison with the conventional approach.

Evolutionary models for the retention of adult–adult social play in primates: The roles of diet and other factors associated with resource acquisition

What factors in animal life history facilitate or reduce the probability that a species will perform play behavior? While some relationships are known within species and across individuals, it is not obvious that such relationships can be used to explain differences and similarities in amount and type of play across large taxonomic groupings of animals, let alone transitions among them. Primates encompass a relatively large assemblage of species that differ in numerous dietary, habitat, reproductive, and physiological processes. While all juvenile primates engage in social play, far fewer primate species engage in social play as adults. Here, derived from theory and more small-scale comparisons, we explore several biological and behavioral phenomena that differ among nonhuman primates and which may explain differences in the occurrence of adult–adult social play. We used phylogenetic logistic regression to assess the correlation of adult play with various life-history, metabolic and socioecological variables. Although the main contribution of our paper is demonstrating use of phylogenetic methods in the context of play evolution, suggestive but not significant evidence was found that adult sexual and nonsexual social play is influenced by diet, habitat, reproductive, and metabolic factors, sometimes in opposite directions, that we discuss along with needed future analyses involving improved data and interactions among traits.

A high-resolution model of bat diversity and endemism for continental Africa

Bats are the second-most species-rich mammal group numbering more than 1270 species globally. Our knowledge of their geographic distributions and diversity patterns however is very limited – possibly the poorest among mammals – mainly due to their nocturnal and volant life history, and challenging fieldwork conditions in the tropics where most bat species occur. This knowledge gap obscures the geographic extent of ecosystem services provided by bats (i.e. pollination, seed dispersal and insect control), translates into inefficient conservation policies, and restricts macroecological analyses to coarse spatial resolutions. In contrast to the currently prevailing method of estimating species distributions using expert-drawn range maps, correlative species distribution models (SDMs) can provide estimates at very fine spatial grains and largely account for widespread sample bias as well as the prevalent Wallacean shortfall in species occurrence data. Very few such studies have hitherto been published that cover a large and complete taxonomic group with fine resolution at continental extent. Using an unparalleled amount of occurrence data, the MaxEnt algorithm and tailored solutions to specific modelling challenges, we created SDMs for nearly all 250 African bat species to explore emerging diversity patterns at a resolution of 1km2. Predicted species richness generally increases towards the equator conforming to expectations. Within the tropical area of elevated richness, several pronounced richness peaks and lows stand out, hinting at a complex interplay of determining factors. Richness gradients are often steep, decreasing strongly away from streams, and especially so in savanna biomes. Species richness also seems positively associated with rugged terrain, in particular at lower elevations. Centres of endemism are found primarily at low latitudes near major elevational ranges. Overlap with hotspots of species richness is rather low, and confined to five or six topodiverse, relatively low lying areas between western Guinea and the East African coast. Several poorly sampled regions are identified that may represent rewarding future survey targets. Our results demonstrate the value of stacking SDMs to infer plausible continent-wide diversity gradients at a spatial resolution fine enough to directly inform conservation policies and to open up new avenues in macroecological research.

Biogeographical Interpretation of Elevational Patterns of Genus Diversity of Seed Plants in Nepal.

This study tests if the biogeographical affinities of genera are relevant for explaining elevational plant diversity patterns in Nepal. We used simultaneous autoregressive (SAR) models to investigate the explanatory power of several predictors in explaining the diversity-elevation relationships shown in genera with different biogeographical affinities. Delta akaike information criterion (ΔAIC) was used for multi-model inferences and selections. Our results showed that both the total and tropical genus diversity peaked below the mid-point of the elevational gradient, whereas that of temperate genera had a nearly symmetrical, unimodal relationship with elevation. The proportion of temperate genera increased markedly with elevation, while that of tropical genera declined. Compared to tropical genera, temperate genera had wider elevational ranges and were observed at higher elevations. Water-related variables, rather than mid-domain effects (MDE), were the most significant predictors of elevational patterns of tropical genus diversity. The temperate genus diversity was influenced by energy availability, but only in quadratic terms of the models. Though climatic factors and mid-domain effects jointly explained most of the variation in the diversity of temperate genera with elevation, the former played stronger roles. Total genus diversity was most strongly influenced by climate and the floristic overlap of tropical and temperate floras, while the influences of mid-domain effects were relatively weak. The influences of water-related and energy-related variables may vary with biogeographical affinities. The elevational patterns may be most closely related to climatic factors, while MDE may somewhat modify the patterns. Caution is needed when investigating the causal factors underlying diversity patterns for large taxonomic groups composed of taxa of different biogeographical affinities. Right-skewed diversity-elevation patterns may be produced by the differential response of taxa with varying biogeographical affinities to climatic factors and MDE.

A Tale of Two Hyper-diversities: Diversification dynamics of the two largest families of lichenized fungi.

Renewed interests in macroevolutionary dynamics have led to the proliferation of studies on diversification processes in large taxonomic groups, such as angiosperms, mammals, and birds. However, such a study has yet to be conducted in lichenized fungi – an extremely successful and diverse group of fungi. Analysing the most comprehensive time-calibrated phylogenies with a new analytical method, we illustrated drastically different diversification dynamics between two hyper-diverse families of lichenized fungi, Graphidaceae and Parmeliaceae, which represent more than a fourth of the total species diversity of lichenized fungi. Despite adopting a similar nutrition mode and having a similar number of species, Graphidaceae exhibited a lower speciation rate, while Parmeliaceae showed a sharp increase in speciation rate that corresponded with the aridification during the Oligocene-Miocene transition, suggesting their adaptive radiation into a novel arid habitat.

Dissolved organic monomer partitioning among bacterial groups in two oligotrophic lakes.

SummaryUnderstanding how resource partitioning works among taxa is crucial in explaining coexistence and competition within a community. Here, we assessed resource partitioning among freshwater bacterial groups from two oligotrophic lakes using four types of organic substrates as compound models. Substrate uptake patterns were examined by microautoradiography combined with catalysed reporter deposition fluorescent in situ hybridization. Four large taxonomic groups were found in the lakes, but A ctinobacteria (AcI lineage) and B etaproteobacteria (R‐BTcluster) dominated the bacterial assemblage. Monomers containing nitrogen and/or phosphorus were preferred over the ones containing only carbon. All groups were able to incorporate amino acids, adenosine triphosphate and glucose. However, acetate was only taken up by ∼ 10–12% of bacteria, and its uptake was not detected in C ytophaga‐F lavobacteria. Apart from acetate, the contribution of a particular bacterial group to the uptake of a substrate was proportional to its relative abundance. In both lakes, we detected substrate partitioning between AcI Actinobacteria, which was overrepresented in glucose and acetate utilization, and R‐BT B etaproteobacteria, which dominated amino acid uptake. Our results strongly point to physiological niche separation of those bacterial groups in alpine lakes.

On the existence and potential functions of low-amplitude vocalizations in North American birds

ABSTRACT Research on acoustic communication has focused predominantly on high-amplitude, long-range vocalizations that are easily recognized from a distance by the human ear. However, attention has recently expanded to the more enigmatic low-amplitude (quiet) vocalizations produced during close-proximity interactions associated with a variety of social behaviors such as aggression, courtship, group movements, and predator avoidance. The existence of low-amplitude vocalizations has been identified in a number of individual avian and nonavian species (e.g., crickets, fish, and primates), but how common these signals are within larger taxonomic groups such as orders and classes remains poorly understood. Here, we used the Birds of North America Online archive to perform a survey of the existence and putative functions of low-amplitude vocalizations across 749 species accounts of breeding birds in North America. By searching with keywords such as soft, quiet, low-amplitude, and whispered, we found evidence th...

Conserved microsatellites in ants enable population genetic and colony pedigree studies across a wide range of species.

Broadly applicable polymorphic genetic markers are essential tools for population genetics, and different types of markers have been developed for this purpose. Microsatellites have been employed as particularly polymorphic markers for over 20 years. However, PCR primers for microsatellite loci are often not useful outside the species for which they were designed. This implies that a new set of loci has to be identified and primers developed for every new study species. To overcome this constraint, we identified 45 conserved microsatellite loci based on the eight currently available ant genomes and designed primers for PCR amplification. Among these loci, we chose 24 for in-depth study in six species covering six different ant subfamilies. On average, 11.16 of these 24 loci were polymorphic and in Hardy-Weinberg equilibrium in any given species. The average number of alleles for these polymorphic loci within single populations of the different species was 4.59. This set of genetic markers will thus be useful for population genetic and colony pedigree studies across a wide range of ant species, supplementing the markers available for previously studied species and greatly facilitating the study of the many ant species lacking genetic markers. Our study shows that it is possible to develop microsatellite loci that are both conserved over a broad range of taxa, yet polymorphic within species. This should encourage researchers to develop similar tools for other large taxonomic groups.

Phylogeny and classification of passerine birds, passeriformes

The paper presents an overview of the current state of studying the phylogeny and evolution of the largest taxonomic group of birds—the order Passeriformes. Phylogenetic relationships and problems of the classification of passerines according to the data of morphological and molecular studies are discussed. All the results on this issue obtained during the past 25 years are considered and summarized.

PUmPER: phylogenies updated perpetually

Summary: New sequence data useful for phylogenetic and evolutionary analyses continues to be added to public databases. The construction of multiple sequence alignments and inference of huge phylogenies comprising large taxonomic groups are expensive tasks, both in terms of man hours and computational resources. Therefore, maintaining comprehensive phylogenies, based on representative and up-to-date molecular sequences, is challenging. PUmPER is a framework that can perpetually construct multi-gene alignments (with PHLAWD) and phylogenetic trees (with ExaML or RAxML-Light) for a given NCBI taxonomic group. When sufficient numbers of new gene sequences for the selected taxonomic group have accumulated in GenBank, PUmPER automatically extends the alignment and infers extended phylogenetic trees by using previously inferred smaller trees as starting topologies. Using our framework, large phylogenetic trees can be perpetually updated without human intervention. Importantly, resulting phylogenies are not statistically significantly worse than trees inferred from scratch.Availability and implementation: PUmPER can run in stand-alone mode on a single server, or offload the computationally expensive phylogenetic searches to a parallel computing cluster. Source code, documentation, and tutorials are available at https://github.com/fizquierdo/perpetually-updated-trees.Contact: Fernando.Izquierdo@h-its.orgSupplementary information: Supplementary Material is available at Bioinformatics online.

The evolution of evolvability in microRNA target sites in vertebrates

The lack of long-term evolutionary conservation of microRNA (miRNA) target sites appears to contradict many analyses of their functions. Several hypotheses have been offered, but an attractive one—that the conservation may be a function of taxonomic hierarchy (vertebrates, mammals, primates, etc.)—has rarely been discussed. For such an analysis, we cannot use evolutionary conservation as a criterion of target identification, and hence, have used high confidence target sites in the cross-linking immunoprecipitation (CLIP) data. Assuming that a proportion, p, of target sites in the CLIP data are conserved, we define the evolvability of miRNA targets as 1-p. Genomic data from vertebrate species show that the evolvability between human and fish is very high, at more than 90%. The evolvability decreases to 50% between birds and mammals, 20% among mammalian orders, and only 6% between human and chimpanzee. Within each taxonomic hierarchy, there is a set of targets that are conserved only at that level of evolution. Extrapolating the evolutionary trend, we find the evolvability in any single species to be close to 0%. Thus, all miRNA target sites identified by the CLIP method are evolutionarily conserved in one species, but the conservation is lost step by step in larger taxonomic groups. The changing evolvability of miRNA targets suggests that miRNA-target interactions may play a role in the evolution of organismal diversity.

Structural Characterization and Chemical Classification of Some Bryophytes Found in Latvia

Bryophytes are the second largest taxonomic group in the plant kingdom; yet, studies conducted to better understand their chemical composition are rare. The aim of this study was to characterize the chemical composition of bryophytes common in Northern Europe by using elemental, spectral, and non-destructive analytical methods, such as Fourier transform IR spectrometry (FT-IR), solid-phase (13) C-NMR spectrometry, and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), for the purpose of investigating their chemotaxonomic relationships on the basis of chemical-composition data. The results of all these analyses showed that bryophytes consist mainly of carbohydrates. Judging by FT-IR spectra, the OH groups in combination of CO groups were the most abundant groups. The (13) C-NMR spectra provided information on the presence of such compounds as phenolics and lipids. It was found that the amount of phenolic compounds in bryophytes is relatively small. This finding definitely confirmed the absence of lignin in the studied bryophytes. Cluster analysis was used to better understand differences in the chemical composition of bryophyte samples and to evaluate possible usage of these methods in the chemotaxonomy of bryophytes.

Thermal and Spectroscopic Characterization of a Proton Pumping Rhodopsin from an Extreme Thermophile

So far retinylidene proteins (∼rhodopsin) have not been discovered in thermophilic organisms. In this study we investigated and characterized a microbial rhodopsin derived from the extreme thermophilic bacterium Thermus thermophilus, which lives in a hot spring at around 75 °C. The gene for the retinylidene protein, named thermophilic rhodopsin (TR), was chemically synthesized with codon optimization. The codon optimized TR protein was functionally expressed in the cell membranes of Escherichia coli cells and showed active proton transport upon photoillumination. Spectroscopic measurements revealed that the purified TR bound only all-trans-retinal as a chromophore and showed an absorption maximum at 530 nm. In addition, TR exhibited both photocycle kinetics and pH-dependent absorption changes, which are characteristic of rhodopsins. Of note, time-dependent thermal denaturation experiments revealed that TR maintained its absorption even at 75 °C, and the denaturation rate constant of TR was much lower than those of other proton pumping rhodopsins such as archaerhodopsin-3 (200 ×), Haloquadratum walsbyi bacteriorhodopsin (by 10-times), and Gloeobacter rhodopsin (100 ×). Thus, these results suggest that microbial rhodopsins are also distributed among thermophilic organisms and have high stability. TR should allow the investigation of the molecular mechanisms of ion transport and protein folding.

Microbial Volatile Emissions as Insect Semiochemicals

We provide a synthesis of the literature describing biochemical interactions between microorganisms and insects by way of microbial volatile organic compound (MVOC) production. We evaluated the functionality and ecological context of MVOC signals, and explored important metabolic pathways involved in MVOC production. The cosmopolitan distribution of microorganisms creates a context for frequent, and frequently overlooked, insect responses to microbial emissions. There are numerous instances of MVOCs being closely associated with insect feeding behaviors, but some MVOCs are also powerful repellants. Emissions from microorganisms in situ may signal aspects of habitat suitability or potential exposure to entomopathogens. In some ecosystems, bacterial or fungal volatiles can also incite insect aggregations, or MVOCs can resemble sexual pheromones that elicit mating and oviposition behaviors from responding insects. A single microorganism or MVOC can have different effects on insect behaviors, especially across species, ontogenies, and habitats. There appears to be a multipartite basis for insect responses to MVOCs, and complex tritrophic interactions can result from the production of MVOCs. Many biochemical pathways for behaviorally active volatile production by microbial species are conserved across large taxonomic groupings of microorganisms. In addition, there is substantial functional redundancy in MVOCs: fungal tissues commonly produce polyketides and short-chain alcohols, whereas bacterial tissues tend to be more commonly associated with amines and pyrazines. We hypothesize that insect olfactory responses to emissions from microorganisms inhabiting their sensory environment are much more common than currently recognized, and that these signals represent evolutionarily reliable infochemicals. Insect chemoreception of microbial volatiles may contribute to the formation of neutral, beneficial, or even harmful symbioses and provide considerable insight into the evolution of insect behavioral responses to volatile compounds.

Haldane's Rule in Marsupials: What Happens When Both Sexes Are Functionally Hemizygous?

During the process of speciation, diverging taxa often hybridize and produce offspring wherein the heterogametic sex (i.e., XY or ZW) is unfit (Haldane's rule). Dominance theory seeks to explain Haldane's rule in terms of the difference in X-linked dominance regimes experienced by the sexes. However, X inactivation in female mammals extends the effects of hemizygosity to both sexes. Here, we highlight where the assumptions of dominance theory are particularly problematic in marsupials, where X inactivation uniformly results in silencing the paternal X. We then present evidence of Haldane's rule for sterility but not for viability in marsupials, as well as the first violations of Haldane's rule for these traits among all mammals. Marsupials represent a large taxonomic group possessing heteromorphic sex chromosomes, where the dominance theory cannot explain Haldane's rule. In this light, we evaluate alternative explanations for the preponderance of male sterility in interspecific hybrids, including faster male evolution, X-Y interactions, and genomic conflict hypotheses.