Lawrence R. Kirkendall

Bark beetles and pinhole borers (Curculionidae, Scolytinae, Platypodinae) alien to Europe

Abstract Invasive bark beetles are posing a major threat to forest resources around the world. DAISIE’s web-based and printed databases of invasive species in Europe provide an incomplete and misleading picture of the alien scolytines and platypodines. We present a review of the alien bark beetle fauna of Europe based on primary literature through 2009. We find that there are 18 Scolytinae and one Platypodinae species apparently established in Europe, from 14 different genera. Seventeen species are naturalized. We argue that Trypodendron laeve, commonly considered alien in Europe, is a native species; conversely, we hypothesize that Xyleborus pfeilii, which has always been treated as indigenous, is an alien species from Asia. We also point out the possibility that the Asian larch bark beetle Ips subelongatus is established in European Russia. We show that there has been a marked acceleration in the rate of new introductions to Europe, as is also happening in North America: seven alien species were first recorded in the last decade. We present information on the biology, origins, and distributions of the alien species. All but four are polyphagous, and 11 are inbreeders: two traits which increase invasiveness. Eleven species are native to Asia, six to the Americas, and one is from the Canary Islands. The Mediterranean is especially favorable for invasives, hosting a large proportion of the aliens (9/19). Italy, France and Spain have the largest numbers of alien species (14, 10 and 7, respectively). We point out that the low numbers for at least some countries is likely due to under-reporting. Finally, we discuss the difficulties associated with identifying newly invasive species. Lack of good illustrations and keys hinder identification, particularly for species coming from Asia and Oceania.

The Costs Of Sex: Facing Real-world Complexities

Understanding the maintenance of sexual reproduction constitutes a difficult problem for evolutionary biologists because of the immediate costs that sex seems to incur. Typically, general benefits to sex and recombination are investigated that might outweigh these costs. However, several factors can strongly influence the complex balance between costs and benefits of sex; these include constraints on the evolution of asexuality, ecological differentiation, and certain life-history traits. We review these factors and their empirical support for the first time in a unified framework and find that they can reduce the costs of sex, circumvent them, or make them inapplicable. These factors can even tip the scales to a net benefit for sex. The reviewed factors affect species and species groups differently, and we conclude consequently that understanding the maintenance of sex could turn out to be more species-specific than commonly assumed. Interestingly, our study suggests that, in some species, no general benefits to sex and recombination might be needed to understand the maintenance of sex, as in our case study of dandelions.

ON THE EVOLUTION OF PSEUDOGAMY

A. density‐ and frequency‐dependent model for the evolution and maintenance of pseudogamous females is developed and analyzed. Ecological as well as evolutionary aspects of pseudogamy are discussed. Criteria are described for the stable coexistence of sexual females and pseudogamous females under natural conditions. The conditions for invasion of a normal bisexual population by pseudogamous females are less stringent than the conditions for stable coexistence. Hence, we expect that some populations will be characterized by unstable sex ratios over time (with the resulting local extinction due to lack of males) while other populations will be characterized by stable sex ratios over time. If high population sex ratios (i.e., many females to few males) are to be stable, the net population growth rate must be large, and there can be no successful male preference for sexual females.

Evolution and Diversity of Bark and Ambrosia Beetles

Abstract We review the morphology, larval feeding habits, reproductive behavior, and social behavior of Scolytinae and Platypodinae. Their morphology and behavior are adaptations to a lifestyle centered on tunneling in wood. Tunnels are easily defended, and dead wood is a relatively long-lasting resource that can support large populations but that is unpredictable in space and time; these features favor the evolution of parental care and more advanced forms of social behavior. Bark and ambrosia beetles are unique among beetles in the extraordinary variety of feeding biologies and mating systems; in particular, regular bigyny has evolved in many lineages, an otherwise unknown animal mating system. Sex role reversal is rare in insects but has evolved repeatedly in bark and ambrosia beetles. Finally, we summarize for the first time diversity patterns of mating systems and feeding biology for the entire Scolytinae world fauna, ca. 6000 species in 247 genera.

Evidence for a new lineage of primary ambrosia fungi in Geosmithia Pitt (Ascomycota: Hypocreales).

Geosmithia is a genus of mitosporic filamentous fungi typically associated with phloeophagous bark beetles world-wide. During this study, the fungal associates of ambrosia beetles Cnesinus lecontei, Eupagiocerus dentipes, and Microcorthylus sp. from Costa Rica, were studied using morphology and DNA sequences. Fungal associates belonged to four undescribed Geosmithia species. Geosmithia eupagioceri sp. nov. and G. microcorthyli sp. nov. are evidently primary ambrosia fungi of their respective vectors E. dentipes and Microcorthylus species. They both have convergently evolved distinct morphological adaptations including the production of large, solitary and globose conidia, and yeast-like cells. Tunnels of C. lecontei contained an undescribed Geosmithia species, but its nutritional importance for its vector is unclear. An auxiliary ambrosia fungus, Geosmithia rufescens sp. nov., was found associated with both G. eupagioceri and the Geosmithia species associated with C. lecontei. G. microcorthyli is genetically quite similar to the phloem-associated Geosmithia sp. 8 from Europe. Large differences in morphology between these two species suggest the rapid co-evolution resulting from the close symbiosis of the former with its beetle host. The ITS rDNA sequences of G. microcorthyli and Geosmithia sp. 8 were not diagnostic, suggesting that alternative markers such as EF-1α, IGS rDNA or β-tubulin should be used, together with morphological and ecological data, for species delimitation in this genus. The primary ambrosia fungi described here are derived from phloem-associated ancestors, and represent two independent lineages of ambrosia fungi in the Hypocreales and a new ecological strategy within Geosmithia.

Extraordinary haplotype diversity in haplodiploid inbreeders: phylogenetics and evolution of the bark beetle genus Coccotrypes.

Regular inbreeding by sib-mating is one of the most successful ecological strategies in the bark beetle family Scolytinae. Within this family, the many species (119) in Coccotrypes are found breeding in an exceptional variety of untraditional woody tissues different from bark and phloem. Species delineation by morphological criteria is extremely difficult, however, as in most other inbreeding groups of beetles, perhaps due to the unusual evolutionary dynamics characterizing sib-mating organisms. Hence, we here performed a phylogenetic analysis using molecular data in conjunction with morphological data to better understand morphological and ecological evolution in this sib-mating group. We used partial DNA sequences from the nuclear gene EF-alpha and the mitochondrial genes 12S and CO1 to elucidate patterns of morphological evolution, haplotype variation, and evolutionary pathways in resource use. Sequence variation was high among species and far above that expected at the species level (e.g., 19% for CO1 within Coccotrypes advena). The tendency for exhaustive sequence variation at deeper nodes resulted in ambiguous reconstructions of the deepest splits. However, all results suggested that species with the broadest diets were clustered in a single derived position-another piece of evidence against specialization as a derived evolutionary feature.

ECOLOGICAL AND EVOLUTIONARY STABILITY OF SPERM-DEPENDENT PARTHENOGENESIS: EFFECTS OF PARTIAL NICHE OVERLAP BETWEEN SEXUAL AND ASEXUAL FEMALES

Pseudogamous females reproduce parthenogenetically but require sperm. We analyze a density‐ and frequency‐dependent model for the ecological and evolutionary stability of bisexual populations exposed to invasion by pseudogamous clones. In particular, we examine the effects of partial niche overlap and asymmetric competition between sexual and asexual forms. The model predicts that for a variety of relative fitness values for asexual females, pseudogamous forms can successfully invade bisexual populations. The probability of successful invasion increases as niche overlap decreases. Furthermore, invaded populations are often likely to be stable; for the parameter values analyzed, only combinations of nearly complete niche overlap and high asexual fitness will lead to extinction. Even such combinations will be stable under pronounced asymmetric competition. Asymmetric competition does not, however, affect the invadability of bisexual populations. The model predicts that stable populations cannot have more than three or four females per male; populations with more biased sex ratios are expected to be unstable. We analyze available sex ratio data for pseudogamous insects, fish, and salamanders, and find significant changes in roughly one‐half of the asexual‐dominated populations, but in only one sexual‐dominated population. This analysis includes previously unpublished data on population sex ratios in a pseudogamous bark beetle, Ips acuminatus. Some asexual‐dominated populations have far more than four females per male, contrary to predictions of the model.

Ecological relationships of a guild of tropical beetles breeding in Cecropia petioles in Costa Rica

Petioles are not usually thought of as a habitat for wood-boring insects. The large, woody leaf petioles of Neotropical Cecropia trees, however, have a diverse coleopterous fauna: 36 beetle species in three subfamilies of Cerambycidae and Curculionidae were recorded from Cecropia leafstalks in Costa Rica. A high percentage of the petioles were colonized by beetles in many patches, though fewer were colonized in sun-exposed sites. Community composition was dependent on forest type, petiole moisture and geographical location, but not on the species of Cecropia. Species of Scolytinae were most abundant though species of Zygopinae and Lamiinae were found regularly. The hostspecific scolytine genus Scolytodes dominated in most localities, although species of Hypothenemnus, Coccotrypes and Xylosanidrus morigerus occurred frequently. Sympatric species of Scolytodes clearly used different parts of the petioles. Brood sizes of scolytine beetles were extremely low, ranging from two to ten offspring on average. However, mortality due to parasitoid wasps or predators was low, and since fresh leaves fall close to the previously fallen ones, mortality due to dispersal may also be low. Thus, large beetle populations can exist despite extremely low brood sizes.

Genetic diversity and biogeography of red turpentine beetle Dendroctonus valens in its native and invasive regions.

Sequences of 479 bp region of the mitochondrial COI gene were applied to detect population genetic diversity and structure of Dendroctonus valens populations. By comparing the genetic diversity between native and invasive populations, it was shown that the genetic diversity of Chinese populations was obviously lower than that of native populations with both indices of haplotype diversity and Neis genetic diversity, suggesting genetic bottleneck occurred in the invasive process of D. valens, and was then followed by a relatively quick population buildup. According to phylogenetic analyses of haplotypes, we suggested that the origin of the Chinese population was from California, USA. Phylogenetic and network analysis of native populations of D. valens revealed strong genetic structure at two distinct spatial and temporal scales in North America. The main cause resulting in current biogeographic pattern was supposedly due to recycled glacial events. Meanwhile, a cryptic species might exist in the Mexican and Guatemalan populations.

Lack of nucleotide variability in a beetle pest with extreme inbreeding

The coffee berry borer beetle Hypothenemus hampei (Ferrari) (Curculionidae: Scolytinae) is the major insect pest of coffee and has spread to most of the coffee‐growing countries of the world. This beetle also displays an unusual life cycle, with regular sibling mating. This regular inbreeding and the population bottlenecks occurring on colonization of new regions should lead to low levels of genetic diversity. We were therefore interested in determining the level of nucleotide variation in nuclear and mitochondrial genomes of this beetle worldwide. Here we show that two nuclear loci (Resistance to dieldrin and ITS2) are completely invariant, whereas some variability is maintained at a mitochondrial locus (COI), probably corresponding to a higher mutation rate in the mitochondrial genome. Phylogenetic analysis of the mitochondrial data shows only two clades of beetle haplotypes outside of Kenya, the proposed origin of the species. These data confirm that inbreeding greatly reduces nucleotide variation and suggest the recent global spread of only two inbreeding lines of this bark beetle.