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The introduction of non‐native species across the world represents a major global challenge. Retracing invasion origin is an important first step in understanding the invasion process, often requiring detailed sampling within the native range. Insect species frequently host Wolbachia, a widespread endosymbiotic bacterium that manipulates host reproduction to increase infected female fitness. Here, we draw on the spatial variation in infection frequencies of an actively spreading Wolbachia strain wCer2 to investigate the invasion origin of the European cherry fruit fly, Rhagoletis cerasi. This pest of cherries was introduced from Europe to North America within the last decade. First, we screen the introduced fly population for the presence of Wolbachia. The introduced populations lack the wCer2 strain and the strongly associated mitochondrial haplotype, suggesting strain absence due to founder effects with invading individuals originating from wCer2‐uninfected native population(s). To narrow down geographic regions of invasion origin, we perform spatial interpolation of the wCer2 infection frequency across the native range and predict the infection frequency in unsampled regions. For this, we use an extensive dataset of R. cerasi infection covering 238 populations across Europe over 25 years, complemented with 14 additional populations analyzed for this study. We find that R. cerasi was unlikely introduced from wCer2‐infected populations in Central and Western Europe. We propose wCer2‐uninfected populations from Eastern Europe and the Mediterranean region as the most likely candidates for the invasion origin. This work utilizes Wolbachia as an indirect instrument to provide insights into the invasion source of R. cerasi in North America, revealing yet another application for this multifaceted heritable endosymbiont. Given the prevalence of biological invasions, rapidly uncovering invasion origins gives fundamental insights into how invasive species adapt to new environments. [ABSTRACT FROM AUTHOR]

The bark beetle Ips typographus (L.) is the most important pest in European Norway spruce forests. Especially after abiotic disturbance events, like storms or snowfall, this beetle can utilise vast amounts of trees with impaired defences, leading to mass outbreaks and further mortality of spruce. In 2018, the 'Vaia' storm damaged huge areas of Norway spruce-dominated forests in the Southern Alps. In the following years, the same regions were additionally affected by heavy snowfalls providing high amounts of suitable material for I. typographus brood establishment and development. Since then, these forests have faced unprecedented population outbreaks of I. typographus with severe effects for forest ecosystems, from both an ecological and an economic perspective. A comprehensive understanding of this beetle's genetic structure, including effects of the last ice ages as well as consequences of current population outbreaks, can give insights into the population dynamics of an eruptive species. Here, we studied the genetic structure of five epidemic populations from the Southern Alps and one from a potential glacial refugium in the Apennines. Our results revealed a low genetic diversity and a weak population structure among all studied locations. In the six analysed populations, four already described haplotypes, belonging to three slightly divergent haplogroups, were found. These haplotypes were evenly distributed among populations, including the potential glacial refugium in the Apennines. High gene flow among populations is probably maintained by the beetle's high dispersal capacity and high population densities, resulting in a panmictic population structure. [ABSTRACT FROM AUTHOR]

Ips typographus (L.) and Pityogenes chalcographus (L.) (Coleoptera: Curculionidae) are two common bark beetle species on Norway spruce in Eurasia. Multiple biotic and abiotic factors affect the life cycles of these two beetles, shaping their ecology and evolution. In this article, we provide a comprehensive and comparative summary of selected life-history traits. We highlight similarities and differences in biotic factors, like host range, interspecific competition, host colonization, reproductive behaviour and fungal symbioses. Moreover, we focus on the species' responses to abiotic factors and compare their temperature-dependent development and flight behaviour, cold adaptations and diapause strategies. Differences in biotic and abiotic traits might be the result of recent, species-specific evolutionary histories, particularly during the Pleistocene, with differences in glacial survival and postglacial recolonization. Finally, we discuss future research directions to understand ecological and evolutionary pathways of the two bark beetle species, for both basic research and applied forest management. [ABSTRACT FROM AUTHOR]

Endosymbiont‐induced cytoplasmic incompatibility (CI) may play an important role in arthropod speciation. However, whether CI consistently becomes associated or coupled with other host‐related forms of reproductive isolation (RI) to impede the transfer of endosymbionts between hybridizing populations and further the divergence process remains an open question. Here, we show that varying degrees of pre‐ and postmating RI exist among allopatric populations of two interbreeding cherry‐infesting tephritid fruit flies (Rhagoletis cingulata and R. indifferens) across North America. These flies display allochronic and sexual isolation among populations, as well as unidirectional reductions in egg hatch in hybrid crosses involving southwestern USA males. All populations are infected by a Wolbachia strain, wCin2, whereas a second strain, wCin3, only co‐infects flies from the southwest USA and Mexico. Strain wCin3 is associated with a unique mitochondrial DNA haplotype and unidirectional postmating RI, implicating the strain as the cause of CI. When coupled with nonendosymbiont RI barriers, we estimate the strength of CI associated with wCin3 would not prevent the strain from introgressing from infected southwestern to uninfected populations elsewhere in the USA if populations were to come into secondary contact and hybridize. In contrast, cytoplasmic–nuclear coupling may impede the transfer of wCin3 if Mexican and USA populations were to come into contact. We discuss our results in the context of the general paucity of examples demonstrating stable Wolbachia hybrid zones and whether the spread of Wolbachia among taxa can be constrained in natural hybrid zones long enough for the endosymbiont to participate in speciation. [ABSTRACT FROM AUTHOR]

In modern wildlife ecology, spatial population genetic methods are becoming increasingly applied. Especially for animal species in fragmented landscapes, preservation of gene flow becomes a high priority target in order to restore genetic diversity and prevent local extinction. Within Central Europe, the Alps represent the core distribution area of the black grouse, Lyrurus tetrix. At its easternmost Alpine range, events of subpopulation extinction have already been documented in the past decades. Molecular data combined with spatial analyses can help to assess landscape effects on genetic variation and therefore can be informative for conservation management. Here, we addressed whether the genetic pattern of the easternmost Alpine black grouse metapopulation system is driven by isolation by distance or isolation by resistance. Correlative ecological niche modeling was used to assess geographic distances and landscape resistances. We then applied regression‐based approaches combined with population genetic analyses based on microsatellite data to disentangle effects of isolation by distance and isolation by resistance among individuals and subpopulations. Although population genetic analyses revealed overall low levels of genetic differentiation, the ecological niche modeling showed subpopulations to be clearly delimited by habitat structures. Spatial genetic variation could be attributed to effects of isolation by distance among individuals and isolation by resistance among subpopulations, yet unknown effects might factor in. The easternmost subpopulation was the most differentiated, and at the same time, immigration was not detected; hence, its long‐term survival might be threatened. Our study provides valuable insights into the spatial genetic variation of this small‐scale metapopulation system of Alpine black grouse. [ABSTRACT FROM AUTHOR]