Diversification process of stag beetles belonging to the genus Platycerus Geoffroy (Coleoptera: Lucanidae) in Japan based on nuclear and mitochondrial genes

Molecular phylogenies of the genus Platycerus in Japan were characterized based on the nuclear 28S ribosomal RNA and mitochondrial cytochrome oxidase subunit I (COI) genes. These analyses, combined with our previous morphological information, revealed a detailed diversification process of Platycerus in Japan, as well as estimates of their divergence times. Japanese species were monophyletic and were inferred to have diverged to the acuticollis species group and all other species ca 1.69 Mya. The acuticollis species group then appeared to split into P. viridicuprus and a group including P. takakuwai, P. albisomni and P. acuticollis ca 1.26 Mya. Other specific divergences have occurred primarily since ca 0.33 Mya. Comparing the molecular trees and the morphological tree, we also found introgression of the COI gene in some species. Genetic divergence of Platycerus has occurred intensely in southwestern Japan.     

Radiation and reticulation: extensive introgressive hybridization in the carabid beetles Ohomopterus inferred from mitochondrial gene genealogy

 In the evolutionary process of an animal lineage, interactions in secondary contacts of differentiated populations and introgressive hybridization may play an important role. In the Japanese islands, the carabid subgenus Ohomopterus (genus Carabus) exhibits a marked differentiation in body size and genital morphology. Although geographical differentiation is apparent, two or three species usually coexist at many localities. Their reproductive isolation relies on body size differences, chemical cues for mate recognition, and a species-specific genital lock-and-key system. However, these isolation mechanisms are not always effective enough to prevent interspecific hybridization. An initial assessment of the species-level phylogeny with mitochondrial gene sequences revealed that the gene genealogy is highly inconsistent with the morphology-based taxonomy. A comparison of mitochondrial and nuclear gene genealogies showed that these are strongly incongruent with each other, while the nuclear gene genealogy is more consistent with traditional taxonomy, indicating the repeated occurrence of introgression of mitochondria across species. Here, two different cases of mitochondrial introgression among Ohomopterus species are described in detail, one for parapatric species and the other for sympatric species. First, mitochondrial haplotypes and sequences were studied in Carabus insulicola and three taxa parapatric with C. insulicola, at least two of which hybridize with C. insulicola naturally. Among the four species studied, directional introgressions of mitochondria across boundary zones were detected. Second, in the Mt. Kongo area in central Honshu, which harbors five species, introgression of mitochondria among four out of the five species was detected, despite the apparent absence of on-going natural hybridization. These inferred cases of mitochondrial introgression indicate that species interactions through hybridization could have played an important role at various stages in the evolution of Ohomopterus. Received: April 12, 2002 / Accepted: October 17, 2002 Acknowledgments I am grateful to Alfried P. Vogler for a long-lasting collaboration in the molecular phylogenetic study of Ohomopterus. R. Ishikawa, K. Kubota, M. Ujiie, Y. Takami, and F. Kusumoto have also collaborated at various stages of this study. Thanks are also due to K. Miyashita, T. Funakoshi, H. Fujimoto, T. Dejima, Y. Nagahata, T. Miyagawa, K. Yodoe, H. Kadowaki, S. Nakamine, Y. Oka, H. Tanaka, T. Tanabe, K. Kusakari, and T. Okumura for their care of specimens. Supported by grants-in-aid from the Japan Society for the Promotion of Science (Nos. 09640748, 11304056).     

Increased genetic divergence between two closely related fir species in areas of range overlap

Because of introgressive hybridization, closely related species can be more similar to each other in areas of range overlap (parapatry or sympatry) than in areas where they are geographically isolated from each other (allopatry). Here, we report the reverse situation based on nuclear genetic divergence between two fir species, Abies chensiensis and Abies fargesii, in China, at sites where they are parapatric relative to where they are allopatric. We examined genetic divergence across 126 amplified fragment length polymorphism (AFLP) markers in a set of 172 individuals sampled from both allopatric and parapatric populations of the two species. Our analyses demonstrated that AFLP divergence was much greater between the species when comparisons were made between parapatric populations than between allopatric populations. We suggest that selection in parapatry may have largely contributed to this increased divergence.     

Reproductive interference between three parapatric species of reptile tick

Summary Reproductive interference between three species of reptile tick, Aponomma hydrosauri, Amblyomma albolimbatum and Amb. limbatum was investigated. Adults of two species attach together on the same lizard hosts in narrow overlap zones at parapatric boundaries between species, providing opportunities for interference. The possibility of reproductive interference was suggested because of similarities in the sexual communication systems.Three forms of interference were found in laboratory experiments. Firstly male movement to search for sexually receptive females was inhibited when females of two species were present on the same host, probably because of signal interference. Secondly, a nonspecific, short range attractant pheromone led males into non-conspecific courtship attempts which reduced the time for conspecific courtships. Thirdly Amb. albolimbatum males physically blocked the genitalia of female Ap. hydrosauri after unsuccessful non-conspecific courtship attempts. Field data showed this behaviour was common in both Amblyomma species after conspecific matings. Reproductive interference would reduce the fitness of each species in sympatry, and may contribute to the maintenance of the narrow parapatric boundaries.     

Ecological correlates of the distribution limits of two poeciliid species along a salinity gradient

Identifying the environmental factors responsible for the formation of a species' distribution limit is challenging because organisms interact in complex ways with their environments. However, the use of statistical niche models in combination with the analysis of phenotypic variation along environmental gradients can help to reduce such complexity and identify a subset of candidate factors. In the present study, we used such approaches to describe and identify factors responsible for the parapatric distribution of two closely‐related livebearer fish species along a salinity gradient in the lowlands of Trinidad, West Indies. The downstream distribution limits of Poecilia reticulata were strongly correlated with the brackish–freshwater interface. We did not observe significant phenotypic variation in life‐history traits for this species when comparing marginal with more central populations, suggesting that abrupt changes in conditions at the brackish–freshwater interface limit its distribution. By contrast, Poecilia picta was present across a wide range of salinities, although it gradually disappeared from upstream freshwater localities. In addition, P. picta populations exhibited an increase in offspring size in localities where they coexist with P. reticulata, suggesting a role for interspecific competition. The parapatric distribution of these two species, suggests that P. reticulata distributions are limited by an abiotic factor (salinity), whereas P. picta is limited by a biotic factor (interspecific competition). Similar parapatric patterns have been previously described in other systems, suggesting they might be a common pattern in nature. © 2013 The Linnean Society of London     

Trophic niche partitioning of cryptic species of long-eared bats in Switzerland: implications for conservation

Dietary niche partitioning is postulated to play a major role for the stable coexistence of species within a community, particularly among cryptic species. Molecular markers have recently revealed the existence of a new cryptic species of long-eared bat, Plecotus macrobullaris, in the European Alps. We studied trophic niches as well as seasonal and regional variations of diet in eight colonies of the three Plecotus species occurring in Switzerland. Faeces were collected monthly from individuals returning to roost after foraging. Twenty-one arthropod categories were recognized from the faeces. All three species fed predominantly on Lepidoptera, which made up 41%, 87% and 88% (means across colonies) of the diet composition of P. auritus, P. macrobullaris and P. austriacus, respectively. The occurrence of numerous fragments of both diurnal and flightless insects in the diet of P. auritus (but rarely in the diet of the other two species) indicates that this species mostly gleans prey from substrates. P. austriacus and P. macrobullaris are more typical aerial feeders. The latter two species have narrow trophic niches, whilst P. auritus has a much broader diet. Comparison of intraspecific and interspecific niche overlaps in P. auritus and P. macrobullaris in sympatry suggests dietary niche partitioning between these two species. In contrast, the high similarity of the trophic niches of P. austriacus and P. macrobullaris, associated with a typical parapatric distribution, indicates competitive exclusion. The best conservation measures are preservation and restoration of habitats offering a high abundance of moths, the major prey of the three Plecotus species.     

Ecology and genetics of hybrid zones in the southern African Pycnonotus bulbul species complex

Lloyd, P., Craig, A.J.F.K., Hulley, P.E., Essop, M.F., Bloomer, P. & Crowe, T.M. 1997. Ecology and genetics of hybrid zones in the southern African Pycnonotus bulbul species complex. Ostrich 68 (2–4): 90–96.

The closely related Blackeyed Bulbul Pycnonotus barbatus, Cape Bulbul P. capensis and Redeyed Bulbul P. nigricans have parapatric to locally sympatric distributions within southern Africa. Extensive hybridization along narrow transition zones between each of the three species pairs is described in a region of the Eastern Cape province, South Africa. The transition zones coincide with ecotones between different vegetation types, which in turn follow escarpments or mountain ranges. The lack of population density depressions within the hybrid zones, together with the variability of the hybrids, suggests the hybrids are viable. Sharp step clines in various phenotypic characters are described across the P. barbatus/P. nigricans hybrid zone. A mtDNA analysis found evidence of possible introgression between P. barbatus and P. capensis. All eight P. barbatus x P. nigricans hybrids analysed possessed P. barbatus mtDNA, suggesting the existence of either positive assortative mating or strong directional selection, but our data are unable to distinguish which. Our results do not support the dynamic-equilibrium model, but are compatible with the bounded-hybrid-superiority model. We conclude that the maintenance of the parapatric distributions of the different taxa is due mainly to differences in environmentally-associated fitness between parental phenotypes or among parental and hybrid phenotypes along an ecotone, with the narrowness of the hybrid zones maintained by the steepness of the environmental gradients crossing them.     

Comparative phylogeography and asymmetric hybridization between cryptic bat species

Cryptic speciation and hybridization are two key processes that affect the origin and maintenance of biodiversity and our ability to understand and estimate it. To determine how these two processes interact, we studied allopatric and sympatric colonies of two cryptic bat species (Eptesicus serotinus and Eptesicus isabellinus) with parapatric distribution in the Iberian Peninsula. These species are the main reservoir for the most commonly rabies virus found in bats in Europe: the European bat Lyssavirus type 1 (EBLV‐1). We used mtDNA and nuclear microsatellite markers to confirm the taxonomic status of both species and to show a more pronounced and geographically based genetic structure in E. isabellinus than in its sibling E. serotinus. Using approximate Bayesian computation (ABC), we inferred rapid range expansion in both species after the Last Glacial Maximum until reaching their present distributions. ABC analysis also supported interspecific differences in genetic diversity and structure, pointing to an earlier expansion of E. isabellinus northward. We found no evidence of mitochondrial introgression between species, but nuclear markers identified a male‐mediated ongoing asymmetric hybridization from E. isabellinus to E. serotinus (28% hybrids in E. serotinus and 5% in E. isabellinus) in the contact zone. Although none of the bats studied tested positive for Lyssavirus RNA, the asymmetric hybridization supports the potential for the recently suggested interspecific transmission of EBLV‐1 from E. isabellinus into E. serotinus.     

Comparative phylogeography of two sibling species of forest‐dwelling rodent (Praomys rostratus and P. tullbergi) in West Africa: different reactions to past forest fragmentation

Two sibling species of the rodent genus Praomys occur in West African forests: P. tullbergi and P. rostratus. By sampling across their geographical ranges (459 individuals from 77 localities), we test the hypothesis that climatic oscillations during the Quaternary made an impact on the observed pattern of cytochrome b sequence variation. We show that, although these two species have parapatric geographical distributions, their phylogeographical histories are dissimilar, which could be related to their distinct ecological requirements. Since the arid phases of the Pleistocene were characterized by isolated forest patches, and intervening wetter periods by forest expansion, these changes in forest cover may be the common mechanism responsible for the observed phylogeographical patterns in both of these species. For example, in both species, most clades had either allopatric or parapatric geographical distributions; however, genetic diversity was much lower in P. tullbergi than in P. rostratus. The genetic pattern of P. tullbergi fits the refuge hypothesis, indicating that a very small number of populations survived in distinct forest blocks during the arid phases, then expanded again with forest recovery. In contrast, a number of populations of P. rostratus appear to have survived during the dry periods in more fragmented forest habitats, with varying levels of gene flow between these patches depending on climatic conditions and forest extent. In addition, historical variations of the West African hydrographic network could also have contributed to the pattern of genetic differentiation observed in both species.     

Mating behaviour and parapatry in two species of Australian reptile tick

Summary Few quantitative studies have examined the ecological consequences of similarities and/or differences in mating behaviour of parapatric species. Reproductive interference occurs between several parapatric species of Australian reptile tick, due to similarities in their mating behaviour (Andrews et al. 1982a). Attempts to determine whether reproductive interference serves to maintain parapatry between Amblyomma limbatum and Aponomma hydrosauri have been hindered because of difficulties in providing conditions conducive to conspecific mating in Amb. limbatum. The present study examined whether off-host and/or onhost temperature influenced the subsequent mating behaviour (i.e. the proportion of females that mate and the time when mating occurs) of these two species. Irrespective of the temperature experienced by ticks prior to host attachment, specific on-host temperatures were needed to induce mating in Amb. limbatum (i.e. host cloacal temperatures >32° C prior to the time of peak mating activity). Significantly more Amb. limbatum females were mated and the time taken by females to mate decreased with increasing on-host temperatures. mating in Ap. hydrosauri occurred over a wider range of on-host temperatures and the time when mating occurred did not alter at different on-host temperatures. In addition, significantly more Ap. hydrosauri males moved and each male made more moves on hosts than did Amb. limbatum males. It is suggested that Ap. hydrosauri may in consequence have a competitive mating advantage over Amb. limbatum at a boundary. Similarities in mating behaviour, on the other hand, increase the probability of reproductive interference, hence reduce the reproductive fitness of colonizing females of both species. We propose that similarities and differences in mating behaviour could play a critical role in the maintenance of parapatric boundaries.     

Morphotypes or distinct species? A multilocus assessment of two East Asian scimitar babblers (Aves,Timaliidae)

In birds, widespread species complexes often exhibit dramatic plumage differences across their distribution, which can give rise to discordance between morphotypes and phylogroups. Accurate identification of species diversity may require an integrated approach in which multilocus genetic data are used for inference and further corroborated by ecological, morphometric or behavioural data. Pomatorhinus gravivox and P. swinhoei, which were formerly considered component races of P. erythrogenys, were recently split using a delimitation system that mainly relied on the quantification of differences in phenotypic traits. We therefore carried out a reassessment of this taxonomic recommendation by conducting phylogenetic and population genetic analyses with multilocus genetic data. A deep mitochondrial split with a Kimura 2-parameter distance of 0.061 was observed, mainly corresponding to the two morphologically defined species. However, one individual from P. swinhoei harboured a haplotype of P. gravivox. Individual-based analyses of nuclear loci identified two distinct clusters that were exactly congruent with the two species. BPP delimitation also provided support for the separation. These congruencies support the notion that these two taxa are best regarded as two separate species. The presence of the P. gravivox mitochondrial haplotype in P. swinhoei was most likely a result of hybridization, due to the clear separation of nuclear loci. The speciation might be attributed to paleoclimatic changes but requires further evaluation due to the likelihood of ecological speciation. This study was in accordance with the results inferred from the quantitative system but highlighted the importance of sampling various data, especially in contact zones, in the study of taxonomy and speciation history.     

Disintegrating over space and time: Paraphyly and species delimitation in the Wehrle's Salamander complex

Accurate species delimitation is critical for biodiversity studies. However, species complexes characterized by introgression, high levels of population structure and subtle phenotypic differentiation can be challenging to delimit. Here, we report on a molecular systematic investigation of the woodland salamanders Plethodon wehrlei and Plethodon punctatus, which traditionally have been placed in the Plethodon wehrlei species group. To quantify patterns of genetic variation, we collected genetic samples from throughout the range of both species, including 22 individuals from nine populations of P. punctatus, and 60 individuals from 26 populations of P. wehrlei. From these samples, we sequenced three mtDNA loci (5596 base pairs) and five nuclear loci (3377 base pairs). We inferred time‐calibrated gene trees and species trees using BEAST 2.4.6, and we delimited putative species using a Bayesian implementation of the general mixed Yule‐coalescent model (bGMYC) and STRUCTURE. Finally, we validated putative species using the multispecies coalescent as implemented in Bayesian Phylogenetics and Phylogeography (BPP). We found substantial phylogeographic diversity in P. wehrlei, including multiple geographically cohesive clades and an inferred mitochondrial common ancestor at 11.5 myr (95% HPD: 9.6–13.6 myr) that separated populations formerly assigned to P. dixi from all other populations. We also found that P. punctatus is deeply nested within P. wehrlei, rendering the latter paraphyletic. After discussing the challenges faced by modern species delimitation methods, we recommend retaining P. punctatus because it is ecologically and phenotypically distinct. We further recommend that P. dixi be recognized as a valid species.     

GENE FLOW AND SPECIES DELIMITATION: A CASE STUDY OF TWO PINE SPECIES WITH OVERLAPPING DISTRIBUTIONS IN SOUTHEAST CHINA

Species delimitation detected by molecular markers is complicated by introgression and incomplete lineage sorting between species. Recent modeling suggests that fixed genetic differences between species are highly related to rates of intraspecific gene flow. However, it remains unclear whether such differences are due to high levels of intraspecific gene flow overriding the spread of introgressed alleles or favoring rapid lineage sorting between species. In pines, chloroplast (cp) and mitochondrial (mt) DNAs are normally paternally and maternally inherited, respectively, and thus their relative rates of intraspecific gene flow are expected to be high and low, respectively. In this study, we used two pine species with overlapping geographical distributions in southeast China, P. massoniana and P. hwangshanensis, as a model system to examine the association between organelle gene flow and variation within and between species. We found that cpDNA variation across these two pine species is more species specific than mtDNA variation and almost delimits taxonomic boundaries. The shared mt/cp DNA genetic variation between species shows no bias in regard to parapatric versus allopatric species’ distributions. Our results therefore support the hypothesis that high intraspecific gene flow has accelerated cpDNA lineage sorting between these two pine species.     

Patterns of species diversity on an oceanic versus a continental island mountain: a hypothesis on species diversification1

Abstract. The vegetation on a wet mountain slope on Haleakala (an oceanic island) is compared with that on Kinabalu (a continental island) to examine relationships between regional floristic richness and α- and β-diversities. The two mountains are similar in their constant tropical climate, generic and family-level floristic elements and geological age of the summit regions, but different in regional floristic richness (rich on Kinabalu vs. poor on Haleakala). α-diversity of canopy and subcanopy tree species was much higher on Kinabalu than in comparable zones on Haleakala. Average turnover rate of species (as logarithmic community similarity) on the slope was one order of magnitude greater on Kinabalu than on Haleakala (0.127 vs. 0.017 per 100 m alt.). While there were genera with wide altitudinal ranges on both mountains, a large proportion of the genera was differentiated into parapatric altitudinal congeners on Kinabalu. By contrast, most genera are altitudinally monotypic on Haleakala. The number of sympatric congeners per genus, and the frequency of multi-specific genera per plot were high on lower slopes but decreased with increasing altitude on Kinabalu, whereas the values were low across all altitudes on Haleakala. These patterns suggest that sympatric and parapatric species radiation was less on Haleakala than on Kinabalu. This may be related to Haleakala's initially poor and disharmonic flora.     

Extensive genetic divergence in the East Asian natricine snake,Rhabdophis tigrinus (Serpentes: Colubridae), with special reference to prominent geographical differentiation of the mitochondrial cytochrome b gene in Japanese populations

We investigated intraspecific phylogenetic relationships in the natricine snake, Rhabdophis tigrinus. A partial sequence of mitochondrial cytochrome b gene (990 bp) was sequenced for 220 individuals from 112 populations. The phylogeny indicated monophyly of the Japanese populations against the continental and Taiwanese populations, sister relationships of the Japanese and continental populations, and monophyly of the whole species. The results strongly suggested substantial genetic divergences among population assemblages from those three regions. We thus consider both lateralis from the continent, which is often synonymized to R. tigrinus, and formosanus from Taiwan, which is usually regarded as a subspecies of the latter, as distinct full species based on the evolutionary species concept. In the Japanese populations, haplotypes were classified to in two major clades (I and II) that were parapatric to each other. Clade I consisted of three distinct subclades (I‐A, I‐B, and I‐C), of which the former two were parapatric with each other, whereas the latter was sympatric with each of the former two subclades. The geographical haplotype structure exhibited by the Japanese populations is likely to have resulted from a series of allopatric differentiations with rapid range extensions of resultant lineages, leading to secondary contact or further admixture of mitochondrial haplotype clades and subclades. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 395–408.     

Molecular phylogeny of the Mediterranean species of Philaenus (Hemiptera: Auchenorrhyncha: Aphrophoridae) using mitochondrial and nuclear DNA sequences

The phylogenies of all eight European species of Philaenus were estimated from cytochrome oxidase subunit I, cytochrome B and internal transcribed spacer 2 (ITS2) fragments of DNA using phylogenetic reconstruction methods: maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) analyses. Based on the topologies of all obtained phylogenetic trees, the monophyly of Philaenus is well supported, being congruent with morphological, ecological and chromosomal data. Three phylogenetic lineages were distinguished in the mitochondrial and combined (mtDNA with ITS2) trees. The first lineage is represented by only one species, Philaenus maghresignus, which inhabits Maghreb and southern Spain. Clade A includes three species: P. tarifa (Southern Iberia), P. italosignus (Sicily and Southern Italy) and P. signatus (the Balkans and Middle East). In clade B two subclades were recognized: B1 represented by P. loukasi (Southern Balkans) and P. arslani (Middle East), and B2 comprising P. spumarus (the most widespread Palaearctic species) and P. tesselatus (from Southern Iberia and Maghreb). These clades were also retrieved in trees reconstructed from nuclear sequences. However, four species (P. maghresignus, P. tarifa, P. italosignus and P. signatus) showed unresolved polytomy at the base of the nuclear tree. Clade A together with P. maghresignus clustered with the ‘signatus’ group defined from morphology, and clade B with the ‘spumarius’ group; these might be considered separate subgenera. Genetic distances in mitochondrial DNA between ingroup species ranged from 14.0% between P. signatus and P. spumarius to 2.4% between P. tesselatus and P. spumarius. By contrast, genetic divergence of ITS2 between ingroup species was very low, at most 2.1%. The divergence of Philaenus species is estimated to have occcurred between 7.9 and 0.6 Ma. Possibly three main speciation events occurred: the first at the Miocene/Pliocene boundary (c. 5.5 Ma) for deeper splits; the second between 4.2 and 2.5 Ma in the Pliocene, when pairs of more closely related species diverged; and the most recent during the Pleistocene glaciations, when the separation of P. tesselatus and P. spumarius took place. The species status of all Philaenus species is confirmed except for P. tesselatus.     

Competition for sites of attachment to hosts in three parapatric species of reptile tick

Summary Competition for sites of attachment to hosts by three species of reptile tick, Aponomma hydrosauri, Amblyomma albolimbatum and Amb. limbatum was investigated as a possible cause for the parapatric distributions found in these species throughout southern Australia. Two localities were chosen for detailed study; a boundary between Ap. hydrosauri and Amb. limbatum near Mt. Mary in the mid-north of South Australia and a boundary between Ap. hydrosauri and Amb. albolimbatum near Arno Bay on the Eyre Peninsula of South Australia. Comparisons of sites of attachment to hosts were made between hosts infested by one species of tick and hosts infested by two species of tick. At Mt. Mary, Ap. hydrosauri and Amb. limbatum adults attach more commonly in the ears and on the midback of their hosts, however, no evidence was found to suggest that competition between the species occurred for these sites. At Arno Bay, Amb. albolimbatum adults had similar sites of attachment to hosts as the other two species, however, significantly more of this species attach in the ears of their hosts. There is no difference in sites of attachment to hosts of Ap. hydrosauri females at Arno Bay and Mt. Mary. Ap. hydrosauri males at Arno Bay, however, show a shift in sites of attachment to hosts away from those sites occupied by Amb. albolimbatum males and females. This shift occurs only in cases where Amb. albolimbatum did not infest the same host. Although the shift in male Ap. hydrosauri sites of attachment to hosts can be explained in terms of past competition, there is no evidence to suggest that such competition in the past, or competition at present, maintains the parapatric boundaries found in these species of thick.     

Resurrection of Mesoplodon hotaula Deraniyagala 1963: A new species of beaked whale in the tropical Indo‐Pacific

We present genetic and morphological evidence supporting the recognition of a previously synonymized species of Mesoplodon beaked whale in the tropical Indo‐Pacific, Mesoplodon hotaula. Although the new species is closely‐related to the rare ginkgo‐toothed beaked whale M. ginkgodens, we show that these two lineages can be differentiated by maternally (mitochondrial DNA), biparentally (autosomal), and paternally (Y chromosome) inherited DNA sequences, as well as by morphological features. The reciprocal monophyly of the mtDNA genealogies and the largely parapatric distribution of these lineages is consistent with reproductive isolation. The new lineage is currently known from at least seven specimens: Sri Lanka (1), Gilbert Islands, Republic of Kiribati (1+), Palmyra Atoll, Northern Line Islands, U.S.A. (3), Maldives (1), and Seychelles (1). The type specimen (Sri Lanka) was described as a new species, M. hotaula, in 1963, but later synonymized with M. ginkgodens. This discovery brings the total number of Mesoplodon species to 15, making it, by far, the most speciose yet least known genus of cetaceans.     

Proposing a new hypothesis: Rickettsia spp. as a mechanism maintaining parapatry between two Australian reptile tick species

This study investigates two parasitic reptile ticks — Bothriocroton hydrosauri and Amblyomma limbatum — of the sleepy lizard (Tiliqua rugosa) that abut at a 1–2 km wide parapatric boundary in South Australia. Long‐term research has investigated potential mechanisms to explain the maintenance of this boundary but has not uncovered why the distribution of A. limbatum does not extend further south. It has been previously hypothesised that pathogens may be responsible for maintaining parapatric boundaries. Rickettsia spp. has previously been reported in B. hydrosauri ticks. This study explored whether Rickettsia spp. occurs in co‐occurring A. limbatum. We observed that Rickettsia spp. was absent from all A. limbatum ticks and that 83% of examined B. hydrosauri were found to be positive with a spotted fever group Rickettsia strain. This study puts forward the hypothesis that Rickettsia spp. could contribute to the maintenance of the Mt Mary parapatric boundary between these two tick species. Further work is required to determine whether Rickettsia spp. can be transmitted from B. hydrosauri to A. limbatum and — if transmission can occur — to explore whether Rickettsia is lethal to A. limbatum ticks.