Genetic inference of orchid colonization of a Costa Rican lava flow

The dispersal and colonization of plant populations allow species to occupy novel habitats, migrate, and undergo range shifts in response to changing environmental factors and, as such, are fundamental ecological processes for ensuring the long-term persistence of species. Natural landscape disturbance often generates habitats available for colonization. Patterns of colonization and population expansion can be inferred from the levels and partitioning of genetic variation of plant populations with known disturbance histories, such as recent volcanic eruptions. We sampled and mapped 496 individuals from two populations of the colonizing terrestrial orchid, Sobralia chrysostoma, on the 1992 lava flow of Volcán Arenal in central Costa Rica. We used neutral co-dominant markers to genotype individuals and estimate population genetic statistics. Both populations had high mean levels of genetic diversity (P = 100%; AP = 3.31; H_e = 0.259) suggesting that the lava flow was colonized by numerous individuals that likely originated from multiple source populations. However, significant spatial genetic structure (SGS) was only present in one population at the smallest distance class (≤2 m) and was low (r = 0.032). That these large and genetically diverse populations had such low SGS and an absence of SGS, respectively is contrary to expectations and differs significantly from the pattern in Epidendrum radicans (Orchidaceae), with which S. chrysostoma is growing sympatrically. Our results suggest that these two populations either consist primarily of immigrant individuals or that seeds produced in situ dispersed over longer distances, thereby producing larger seed shadows and greater overlap of seed shadows.     

Perturbation pathways affecting the avian lotic predator, blue duck, following a volcanic eruption

1. Perturbation pathways affecting interactions between feeding habitat, food supplies and diet of a lotic avian predator, blue duck (Hymenolaimus malacorhynchos Gemlin), were tracked in a New Zealand river following substantial inputs of sediment from a volcanic eruption. Sediment impacts were separated temporally into two distinct phases: (i) deposition of fine ash from volcanic fall‐out, and (ii) pulsed releases of volcanic sand and gravel retained by an upstream dam. 2. Levels of interstitial suspendable inorganic sediments increased by several orders of magnitude following ash inputs to the river, but returned to low levels within 3 months. Flushing of volcanic sand and gravel retained by the dam resulted in sediment deposition upstream of a large island where coarse material lodged firmly between larger benthic substratum elements in blue duck feeding habitat. 3. Changes in algal biomass appeared to largely reflect seasonal and hydrological influences, but the percentage inorganic content of periphyton increased significantly during both posteruption phases. 4. Diversity and abundance of blue duck food supplies on boulders and on the riverbed declined following the eruption, whereas significant impacts on biomass were only detected in benthic habitats which were more susceptible to sediment deposition. However, percent composition of the benthic and boulder invertebrate food resources appeared largely unaffected by the eruption. 5. There was no apparent association between the eruption and the composition or electivity (E*) of blue duck diet, but there was a significant increase in the percent inorganic content of faeces, suggesting a reduction in the quality of food rations. 6. Changes in food quantity and quality associated with deposition of volcanic sediments were linked to an observed decline in blue duck population density and fecundity following the eruption. An interacting continuum of adaptive responses to perturbation intensity and impact duration is proposed for blue duck, and potentially other long‐lived, riverine birds, that enable them to cope with disturbances in highly variable and heterogenous lotic environments.     

Vegetation dynamics under residual large trees following a volcanic eruption in a Valdivian temperate rainforest

Plant Ecology - Airborne volcanic ejecta (tephra) can strongly influence forest ecosystems through initial disturbance processes and subsequent ecological response. Within a tephra-disturbed...     

Rapid evolution and specialization following host colonization in a yucca moth

Host shifts followed by specialization can result in sympatric genetic differentiation, and may have fuelled the diversification of phytophagous insects. This study examines a recent colonization of a non‐native host by Prodoxus quinquepunctellus (Lepidoptera: Prodoxidae). Allozyme differentiation was detected among different host feeding populations, yet was nearly absent among similar host feeding populations in sympatry. Geographical patterns of allozyme variation showed a much higher level of population structure among populations feeding on the derived host. Conversely, mtDNA haplotype frequencies were nearly homogeneous in the derived populations compared to the ancestral populations, suggesting a bottleneck and/or rapid fixation of haplotypes following host colonization. Moth emergence coincided with host plant flowering, and phenological differences between host species translated into allochronic isolation between populations feeding on different hosts. Derived moth populations also differed significantly in three ovipositor characters from ancestral populations. These findings suggest rapid host‐specific genetic differentiation, and specialization of moth emergence time and ovipositor morphology following host colonization.     

Rapid appearance of epistasis during adaptive divergence following colonization

Theory predicts that short-term adaptation within populations depends on additive (A) genetic effects, while gene-gene interactions 'epistasis (E)' are important only in long-term evolution. However, few data exist on the genetic architecture of adaptive variation, and the relative importance of A versus non-additive genetic effects continues to be a central controversy of evolutionary biology after more than 70 years of debate. To examine this issue directly, we conducted hybridization experiments between two populations of wild soapberry bugs that have strongly differentiated in 100 or fewer generations following a host plant shift. Contrary to expectation, we found that between-population E and dominance (D) have appeared quickly in the evolution of new phenotypes. Rather than thousands of generations, adaptive gene differences between populations have evolved in tens. Such complex genetic variation could underlie the seemingly extreme rates of evolution that are increasingly reported in many taxa. In the case of the soapberry bug, extraordinary ecological opportunity, rather than mortality, may have created hard selection for genetic variants. Because ultimate division of populations into genetic species depends on epistatic loss of hybrid compatibility, local adaptation based on E may accelerate macro-evolutionary diversification.     

Nematode succession at deep-sea hydrothermal vents after a recent volcanic eruption with the description of two dominant species

Nematodes are very common in the deep sea and are an important component of deep-sea hydrothermal vent communities. In early 2006, the eruption of the underwater volcano at 9°50’N East Pacific Rise wiped out almost the entire faunal communities of the area. This provided us with the opportunity to study nematode primary succession at vents as well as on adjacent seafloor basalt. Nematode abundance and richness were extremely low at all studied sites in late 2006 and 2007, and increased only slightly in 2009. Interestingly, the most abundant species during early succession were also prominent in this area prior to the eruption. Our results show that nematodes are extremely influenced by volcanic eruptions and need a long period of time to colonize the lava-flooded area in greater numbers and richness. We hypothesize that low food availability on the young bare basalt and harsh environmental conditions at early succession vent sites might hinder a more successful nematode establishment. In addition to the newly established active vent sites we also studied an inactive vent site that was not directly hit by the eruption but whose vent fluid had ceased after the eruption. At this inactive and older vent, diversity was also relatively low but was higher than at the younger, newly established sites. In addition to the ecological analyses, we here describe the two most abundant species found at inactive vents, namely Neochromadora aff. poecilosoma De Mann 1893 and Linhomoeus caudipapillosus sp. n.     

Morphological variation in Gallotia atlantica from the volcanic island of Lanzarote: subspecies designations and recent lava flows

A detailed uni‐ and multivariate analysis of within‐island geographical variation in scalation and body dimensions of the lacertid lizard, Gallotia atlantica, from Lanzarote (and two neighbouring offshore islets) was carried out. Two main morphological groupings were detected: four populations clustered within a putative malpaís group, i.e. from relatively recent volcanic lava fields (seven populations were sampled from these areas), while the other 19 populations (including the three remaining malpaís populations, and those from the offshore islets of Montaña Clara and Alegranza) also clustered together. Thus, while there is a tendency for occupation of malpaís areas to be related to morphological variation, this model does have some inconsistencies. The differentiated malpaís group comprises populations from two geographically isolated areas, one from the central‐western part of the island (Timanfaya) and the other from the north (Malpaís de la Corona). The divergence of these populations is considered to have arisen recently, rather than their being relicts of an ancient, formerly widespread, lineage. The morphological variation partially supports the previous use of two different subspecies to describe the within‐island variation. However, if such a scheme were applied then one of the subspecies would need to encompass populations from the geographically separated southern Timanfaya and Malpaís de la Corona areas, as opposed to just the latter. We reject previous observations that either malpaís individuals in general, or those corresponding to the north‐eastern subspecies, are larger than individuals from other areas. The pattern of morphological variation of G. atlantica within Lanzarote is less pronounced but shows some similarities with patterns of morphological variation in lizards from neighbouring islands. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 395–406.     

Rapid evolution of hybrid breakdown following recent divergence with gene flow in Senecio species on Mount Etna,Sicily

How do nascent species evolve reproductive isolation during speciation with on-going gene flow? How do hybrid lineages become stabilised hybrid species? While commonly used genomic approaches provide an indirect way to identify species incompatibility factors, synthetic hybrids generated from interspecific crosses allow direct pinpointing of phenotypic traits involved in incompatibilities and the traits that are potentially adaptive in hybrid species. Here we report the analysis of phenotypic variation and hybrid breakdown in crosses between closely-related Senecio aethnensis and S. chrysanthemifolius, and their homoploid hybrid species, S. squalidus. The two former species represent a likely case of recent (<200 ky) speciation with gene flow driven by adaptation to contrasting conditions of high- and low-elevations on Mount Etna, Sicily. As these species form viable and fertile hybrids, it remains unclear whether they have started to evolve reproductive incompatibility. Our analysis represents the first study of phenotypic variation and hybrid breakdown involving multiple Senecio hybrid families. It revealed wide range of variation in multiple traits, including the traits previously unrecorded in synthetic hybrids. Leaf shape, highly distinct between S. aethnensis and S. chrysanthemifolius, was extremely variable in F₂ hybrids, but more consistent in S. squalidus. Our study demonstrates that interspecific incompatibilities can evolve rapidly despite on-going gene flow between the species. Further work is necessary to understand the genetic bases of these incompatibilities and their role in speciation with gene flow.Subject terms: Speciation, Plant evolution     

Initial colonization,erosion and accretion of coral substrate

Blocks cut from Porites lutea were laid on the fore reef slope, reef flat and a lagoonal patch reef at Lizard Island, in the Northern Great Barrier Reef, and replicates removed from each environment at intervals of three months over a period of one and a half years. Variations in bioeroders and bioaccretors were noted. Microfaunas are far more numerous than macrofaunas as block colonizers; the principal borers are polychaete worms, whereas encrusters are molluscs, bryozoans, serpulids and solitary corals. The reef slope is more readily colonised by microfauna pioneer communities than are the other areas. All the environments exhibit a change from cirratulids to either sabellids or spionids (polydorids) over the length of the experiment. Accretion occurred on all blocks during the experiment, with significant differences detectable between environments; both reef slope and reef flat blocks showed weight increases of 9–10% whereas blocks from the patch reef showed increases of 15%. Annual erosion rates produced by polychaete worms are 0.694 kg m^-2 year^-1 (reef front), 0.843 kg m^-2 year^-1 (reef flat) and 1.788 kg m^-2 year^-1 (patch reef).     

Seedling establishment ofCastanopsis cuspidata var.sieboldii andPersea thunbergii on lava and scoria of the 1962 eruption on Miyake-jima Island,the Izu Islands

Seedling establishment ofCastanopsis cuspidata var.sieboldii Nakai andPersea thunbergii Kosterm. (Machilus thunbergii Sieb. et Zucc.) in early succession was studied on the lava and the scoria of the 1962 eruption on Miyake-jima Island of the Izu Islands. While tall individuals (> 1 m) ofP. thunbergii were found on both the lava and the scoria, those ofC. cuspidata (> 1 m) were found only on the lava. The height growth rate ofC. cuspidata was very low on the scoria, and there was no individual ofC. cuspidata taller than 0.4 m on the scoria. The proportion of yellow leaved individuals was much higher (37.1%) inC. cuspidata than inP. thunbergii (4.0%) on the scoria, while it was similar between the two species on the lava.Persea thunbergii seemed to be able to establish on both the lava and the scoria, butC. cuspidata established only on the lava. The differences in growth rate and vigor between the two species on the lava and the scoria in early succession may influence later stages of succession.     

Rapid changes in genetic architecture of behavioural syndromes following colonization of a novel environment

Behavioural syndromes, that is correlated behaviours, may be a result from adaptive correlational selection, but in a new environmental setting, the trait correlation might act as an evolutionary constraint. However, knowledge about the quantitative genetic basis of behavioural syndromes, and the stability and evolvability of genetic correlations under different ecological conditions, is limited. We investigated the quantitative genetic basis of correlated behaviours in the freshwater isopod Asellus aquaticus. In some Swedish lakes, A. aquaticus has recently colonized a novel habitat and diverged into two ecotypes, presumably due to habitat‐specific selection from predation. Using a common garden approach and animal model analyses, we estimated quantitative genetic parameters for behavioural traits and compared the genetic architecture between the ecotypes. We report that the genetic covariance structure of the behavioural traits has been altered in the novel ecotype, demonstrating divergence in behavioural correlations. Thus, our study confirms that genetic correlations behind behaviours can change rapidly in response to novel selective environments.     

Patterns of colonization, evolution and gene flow in species of the genus Patella in the Macaronesian Islands

The study of phylogeographical patterns may contribute to a better understanding of factors affecting the dispersal of organisms in ecological and historical times. For intertidal organisms, islands are particularly suitable models allowing the test of predictions related to the efficacy of pelagic larvae dispersal. Here, we study the phylogeographical patterns and gene flow within three groups of species of the genus Patella present in the Macaronesian Islands that have been previously shown to be monophyletic. The genetic variability of around 600 bp of the mitochondrial gene cytochrome c oxidase subunit I was studied by single strand conformation polymorphism and/or sequencing for seven species of limpets. A total of 420 samples were analysed from the Macaronesian archipelagos, North Africa, and Atlantic and Mediterranean shores of the Iberian Peninsula. No clear geographical pattern or temporal congruence was found between the three groups of species, pointing to independent histories and colonization events. However, for the three groups, the split between the Macaronesian and the mainland forms most probably occurred before 3.9 million years ago, predating the establishment of the current circulation patterns. The presence of pelagic larvae in these species is shown to be insufficient to ensure gene flow between continental and Macaronesian populations and between the Macaronesian archipelagos. In the endangered Azorean populations of Patella candei, there is restricted gene flow to Flores and Graciosa.     

The recovery of coral genetic diversity in the Sunda Strait following the 1883 eruption of Krakatau

Surveys of microsatellite variation show that genetic diversity has largely recovered in two reef-building corals, Pocillopora damicornis and Seriatopora hystrix (Scleractinia: Pocilloporidae), on reefs which were decimated by the eruption of the volcano Krakatau in 1883. Assignment methods and gene flow estimates indicate that the recolonization of Krakatau occurred mainly from the closest upstream reef system, Pulau Seribu, but that larval input from other regions has also occurred. This pattern is clearer in S. hystrix, which is traditionally the more dispersal-limited species. Despite these observed patterns of larval dispersal, self-recruitment appears to now be the most important factor in supplying larvae to coral populations in Krakatau. This suggests that the colonization of devastated reefs can occur quickly through larval dispersal; however, their survival requires local sources of larvae for self-recruitment. This research supports the observation that the recovery of genetic diversity in coral reef animals can occur on the order of decades and centuries rather than millennia. Conservation measures aimed at sustaining coral reef populations in Krakatau and elsewhere should include both the protection of upstream source populations for larval replenishment should disaster occur as well as the protection of large adult colonies to serve as local larval sources.     

Impacts of a volcanic eruption on the forest bird community of Montserrat, Lesser Antilles

Volcanic eruptions are an important and natural source of catastrophic disturbance to ecological communities. However, opportunities to study them are relatively rare. Here we report on the effects of the eruption of the Soufrière Hills volcano on the forest bird community of the Lesser Antillean island of Montserrat. The island's species-poor avifauna includes 11 restricted-range species, including the Critically Endangered endemic Montserrat Oriole Icterus oberi . Analysis of monitoring data from 1997 to 2005 indicates that counts of most species were substantially lower following major ashfalls. However, this effect was short-lived, with rapid population recovery in subsequent years. Furthermore, levels of seasonal rainfall appear to have been at least as important in determining population trends as ashfall. Overall, most species were at least as abundant at the end of the study as at the start, and no forest bird species have been extirpated from Montserrat. We discuss potential ecological drivers of ashfall impacts on populations: there is some evidence that terrestrial foragers were most severely affected.     

Organic matter quantity and source affects microbial community structure and function following volcanic eruption on Kasatochi Island,Alaska

In August 2008, Kasatochi volcano erupted and buried a small island in pyroclastic deposits and fine ash; since then, microbes, plants and birds have begun to re‐colonize the initially sterile surface. Five years post‐eruption, bacterial 16S rRNA gene and fungal internal transcribed spacer (ITS) copy numbers and extracellular enzyme activity (EEA) potentials were one to two orders of magnitude greater in pyroclastic materials with organic matter (OM) inputs relative to those without, despite minimal accumulation of OM (< 0.2%C). When normalized by OM levels, post‐eruptive surfaces with OM inputs had the highest β‐glucosidase, phosphatase, NAGase and cellobiohydrolase activities, and had microbial population sizes approaching those in reference soils. In contrast, the strongest factor determining bacterial community composition was the dominance of plants versus birds as OM input vectors. Although soil pH ranged from 3.9 to 7.0, and %C ranged 100×, differentiation between plant‐ and bird‐associated microbial communities suggested that cell dispersal or nutrient availability are more likely drivers of assembly than pH or OM content. This study exemplifies the complex relationship between microbial cell dispersal, soil geochemistry, and microbial structure and function; and illustrates the potential for soil microbiota to be resilient to disturbance.