Phylogeography and species biogeography of montane Great Basin stoneflies

Sky islands are ideal systems for determining the effects of climatic oscillations on species distributions and genetic structure. Our study focused on montane stonefly populations in the Great Basin of western North America. We used niche-based distribution modelling, phylogeography and traditional species-based biogeography to test several hypotheses as follows: (i) genetic differentiation among Doroneuria baumanni populations will be independent of hydrologic connectivity (headwater model); (ii) Sky islands were colonized when habitat was more continuous and populations likely experienced multiple expansions and contractions; (iii) Colonization events were coincident with the late Pleistocene and Holocene; and (iv) Shared topography and climate history will result in concordant patterns of genetic differentiation in D. baumanni and occurrences of 32 stonefly species across the region. Overall, Φ(ST) 's and coalescent-based estimates of migration were consistent with the headwater model. Maximum likelihood and Bayesian gene trees identified three major nonoverlapping east-west clades. Distribution modelling indicated more suitable habitat in the Great Basin during the Last Glacial Maximum than at present, but none during the last interglacial period. Demographic analyses showed evidence of population expansion in one of the three major east-west clades. Intra-clade divergence times (60,000-183,000ybp) were well within the late Pleistocene while among-clade divergence times (499.000-719,000ybp) were deeper. Genetic differentiation in D. baumanni and distributions of stonefly species were significantly concordant. These results imply that climatic oscillations have played major roles in shaping the genetic structure and distributions of Great Basin stoneflies, but that divergence among clades occurred much earlier than our late Pleistocence/early Holocene predictions.     

Phylogeography of the longhorn cactus beetle Moneilema appressum LeConte (Coleoptera: Cerambycidae): was the differentiation of the Madrean sky islands driven by Pleistocene climate changes?

Although it has been suggested that Pleistocene climate changes drove population differentiation and speciation in many groups of organisms, population genetic evidence in support of this scenario has been ambiguous, and it has often been difficult to distinguish putative vicariance from simple isolation by distance. The sky island communities of the American Southwest present an ideal system in which to compare late Pleistocene range fragmentations documented by palaeoenvironmental studies with population genetic data from organisms within these communities. In order to elucidate the impact of Pleistocene climate fluctuations on these environments, biogeographic patterns in the flightless longhorn cactus beetle, Moneilema appressum were examined using mitochondrial DNA sequence data. Gene tree relationships between haplotypes were inferred using parsimony, maximum-likelihood, and Bayesian analysis. Nested clade analysis, Mantel tests, and coalescent modelling were employed to examine alternative biogeographic scenarios, and to test the hypothesis that Pleistocene climate changes drove population differentiation in this species. The program mdiv was used to estimate migration and divergence times between populations, and to measure the statistical support for isolation over ongoing migration. These analyses showed significant geographic structure in genetic relationships, and implicated topography as a key determinant of isolation. However, although the coalescent analyses suggested that a history of past habitat fragmentation underlies the observed geographic patterns, the nested clade analysis indicated that the pattern was consistent with isolation by distance. Estimated divergence times indicated that range fragmentation in M. appressum is considerably older than the end of the most recent glacial, but coincided with earlier interglacial warming events and with documented range expansions in other, desert-dwelling species of Moneilema.     

When North and South don’t mix: genetic connectivity of a recently endangered oceanic cycad,Cycas micronesica,in Guam using EST‐microsatellites

Subject to environmental changes and recurrent isolation in the last ca. 250 Ma, cycads are often described as relicts of a previously common lineage, with populations characterized by low genetic variation and restricted gene flow. We found that on the island of Guam, the endemic Cycas micronesica has most of the genetic variation of 14 EST‐microsatellites distributed within each of 18 genetic populations, from 24 original sampling sites. There were high levels of genetic variation in terms of total number of alleles and private alleles, and moderate levels of inbreeding. Restricted but ongoing gene flow among populations within Guam reveals a genetic mosaic, probably more typical of cycads than previously assumed. Contiguous cycad populations in the north of Guam had higher self‐recruitment rates compared to fragmented populations in the south, with no substantial connection between them except for one population. Guam’s genetic mosaic may be explained by the influence of forest continuity, seed size, edaphic differences, and human transport of cycads. Also important are the extent of synchrony among flushes of reproductive female seed‐bearing sporophylls and restricted pollen movement by an obligate mutualist and generalist insects. An NADH EST‐locus under positive selection may reflect pressure from edaphic differences across Guam. This and three other loci are ideal candidates for ecological genomic studies. Given this species’ vulnerability due to the recent introduction of the cycad aulacaspis scale, we also identify priority populations for ex situ conservation, and provide a genetic baseline for understanding the effects of invasive species on cycads in the Western Pacific, and islands in general.     

ORIGINAL ARTICLE: Mass extinctions in the Azores during the last glaciation: fact or myth?

Aim The influence of the last glaciation on the shallow‐water marine malacofauna of the Azores Islands is reviewed. We test, for this fauna, the ‘Pleistocene temperature theory’ of J.C. Briggs, which hypothesizes that a (supposed) lack of endemics in the older (Azorean endemic) fauna resulted from extinctions caused by a severe drop in sea surface temperatures during the Pleistocene. Location Santa Maria Island, Azores, Portugal. Methods We compare the fossil mollusc fauna of Prainha, Praia do Calhau and Lagoinhas Pleistocene outcrops with the recent mollusc fauna of the Azores Islands. We dated the fossil fauna, using shells of Patella aspera Röding, 1798, by standard U/Th methodology at the GEOTOP laboratory (Université du Québec à Montreal, Canada). Results Dating of the shells of P. aspera indicates that the deposition of the lower unit of the Prainha outcrop corresponded to Marine Oxygen Isotope Substage 5e (MISS 5e). Not a single endemic Azorean species of mollusc that is present in the Pleistocene fossil record has since become extinct, and we found no signs of ‘mass extinctions’ in the littoral marine molluscs of the Azores. The only species that were extirpated from these islands were thermophilic molluscs and littoral bivalves living in fine sand. Main conclusions Our results do not support Briggs’‘Pleistocene temperature theory’. Nor did we find evidence supporting the hypothesis that most of the marine organisms now present in the Azores recolonized the islands after the last glacial maximum.     

Evidence for competitive dominance of Pink salmon (<Emphasis Type="Italic">Oncorhynchus gorbuscha</Emphasis>) over other Salmonids in the North Pacific Ocean

Relatively little is known about fish species interactions in offshore areas of the world’s oceans because adequate experimental controls are typically unavailable in such vast areas. However, pink salmon (Oncorhynchus gorbuscha) are numerous and have an alternating-year pattern of abundance that provides a natural experimental control to test for interspecific competition in the North Pacific Ocean and Bering Sea. Since a number of studies have recently examined pink salmon interactions with other salmon, we reviewed them in an effort to describe patterns of interaction over broad regions of the ocean. Research consistently indicated that pink salmon significantly altered prey abundance of other salmon species (e.g., zooplankton, squid), leading to altered diet, reduced total prey consumption and growth, delayed maturation, and reduced survival, depending on species and locale. Reduced survival was observed in chum salmon (O. keta) and Chinook salmon (O. tshawytscha) originating from Puget Sound and in Bristol Bay sockeye salmon (O. nerka). Growth of pink salmon was not measurably affected by other salmon species, but their growth was sometimes inversely related to their own abundance. In all marine studies, pink salmon affected other species through exploitation of prey resources rather than interference. Interspecific competition was observed in nearshore and offshore waters of the North Pacific Ocean and Bering Sea, and one study documented competition between species originating from different continents. Climate change had variable effects on competition. In the North Pacific Ocean, competition was observed before and after the ocean regime shift in 1977 that significantly altered abundances of many marine species, whereas a study in the Pacific Northwest reported a shift from predation- to competition-based mortality in response to the 1982/1983 El Nino. Key traits of pink salmon that influenced competition with other salmonids included great abundance, high consumption rates and rapid growth, degree of diet overlap or consumption of lower trophic level prey, and early migration timing into the ocean. The consistent pattern of findings from multiple regions of the ocean provides evidence that interspecific competition can significantly influence salmon population dynamics and that pink salmon may be the dominant competitor among salmon in marine waters.     

If hippopotamuses cannot swim,how did they colonize islands?

Owing to their aquatic lifestyle, hippopotamuses are normally believed to have reached islands by swimming. Yet, some studies suggest they cannot swim due to their relatively high density. If so, this raises the question of how hippopotamuses would have reached some islands. Their immigration into the British Isles, Sicily, Malta, Zanzibar and Mafia can be accounted for, because these islands sit on continental shelves and were often linked to the mainland during the Pleistocene glacio‐eustatic sea‐level falls. In contrast, their occurrence in Crete, Cyprus and Madagascar would be more difficult to explain. Available geological evidence does not seem to rule out that the latter islands might have been connected with the nearest mainland areas in very recent times. This study intends to consider possibilities about how hippopotamuses reached islands and to show that more effective collaboration is required among specialists involved with the study of insular evolution, colonization and speciation.     

Belowground carbon storage of Micronesian mangrove forests

Belowground carbon storage was examined for mangrove forests on Pohnpei Island, Micronesia. Stored carbon in a coral reef-type mangrove habitat consisting of a 2 m thick mangrove peat layer, which is a type of mangrove habitat in tropical Pacific islands, was estimated at 1300 t C ha^–1. The carbon burial rate during the phase of gradual sea-level rise, which was calculated at 93 g m^–2 year^–1 between 1800 and 1380 years bp using the medians of the radiocarbon ages, was significantly higher than that between 1380 years bp and present in a stable sea-level phase.