The tempo of trait divergence in geographic isolation: Avian speciation across the Marañon Valley of Peru

Geographic isolation is considered essential to most speciation events, but our understanding of what controls the pace and degree of phenotypic divergence among allopatric populations remains poor. Why do some taxa exhibit phenotypic differentiation across barriers to dispersal, whereas others do not? To test factors controlling phenotypic divergence in allopatry, we employed a comparative phylogeographic approach consisting of replicates of ecologically similar Andean bird species isolated across a major biogeographic barrier, the Marañon Valley of Peru. Our study design leverages variation among codistributed taxa in their degree of plumage, morphometric, and vocal differentiation across the Marañon to examine the tempo of phenotypic evolution. We found that substantial plumage differences between populations required roughly two million years to evolve. In contrast, morphometric trait evolution showed greater idiosyncrasy and stasis. Our results demonstrate that despite a large degree of idiosyncrasy in the relationship between genetic and phenotypic divergence across taxa and environments, comparative studies within regions may reveal predictability in the pace of phenotypic divergence. Our results also suggest that social selection is important for driving differentiation of populations found in similar environments.     

Nectar provision attracts hummingbirds and connects interaction networks across habitats

Many ecosystems have been modified by humans, creating novel habitats that include human-provided resources. Gardens adjacent to native habitats may affect plant–pollinator interactions by altering the determinants of interactions and species specialization. Here, we characterized a network comprising plants and hummingbirds interacting in a birdwatching garden with human-provided resources (nectar feeders and exotic plants) and adjacent Andean cloud forest in Colombia. Specifically, we investigated the proportion of hummingbirds visiting feeders and native/exotic plants to evaluate the connection between the habitats and the ecological determinants of the interaction network. Hummingbirds relied heavily on artificial nectar feeders in the garden, leaving the natural cloud forest for resources. Morphological matching was the single most important predictor of the observed pairwise interactions, for both hummingbirds and plants. At the species level, longer flowering phenology and a higher amount of sugar in nectar led to a higher degree for plants (i.e. the number of visiting hummingbird species). In contrast, a longer floral corolla was associated with lower specialization. Abundance was the best predictor of the number of partners for hummingbirds. The garden created for birdwatching attracted most, but not all, hummingbird species beyond their natural cloud forest habitat. Interestingly, the most frequently visited plants in the garden were native, especially the endemic and endangered tree Zygia lehmannii (Fabaceae). Our results show that some ecological mechanisms determining interactions in natural communities still hold in intensively modified habitats. Furthermore, a compromise between conservation and hummingbirds’ attraction to birding lodges/gardens is possible, for instance by favouring native and endemic plant species that are highly attractive for pollinators.     

Cultivable fungal community associated with the tropical orchid Dichaea andina

The orchid–fungus relationship has been studied since the discovery that the minute seeds of orchids depend on fungi to support the germination process. With the aim of describing the biodiversity of cultivable endophytic and mycorrhizal fungi from the orchid Dichaea andina, we isolated pure fungal cultures from its roots and identified them by sequencing the internal transcribed spacer. We recorded 22 fungal operational taxonomic units belonging to eight orders of Ascomycota: Eurotiales, Hypocreales, Xylariales, Helotiales, Boliniales, Chaetothyriales, Chaetosphaeriales and Pleosporales. The only Basidiomycota isolated belonged to the genus Ceratobasidium from the order Cantharellales, whose members are known as orchid mycorrhizal fungi. At the genus level, we identified 16 genera, the most common of which were Byssochlamys, Camarops, Trichoderma, Cladophialophora, Fusarium and Xylaria; some of them had been reported previously as orchid endophytes. The relevance of endophytic fungi to their hosts is still unclear, but this widely distributed interaction deserves further investigation.     

Rarity up in the mountain: Ecological niche modeling,phenology, and reproductive biology of the most commercialized Masdevallia species

Knowledge of how natural and anthropogenic factors can limit the distribution of rare species is key to develop conservation strategies. We show data on how both factors potentially affect the distribution of a rare high Andean orchid. We chose Masdevallia coccinea as a model because it is endangered and the most commercialized species of the entire genus. Using ecological niche modeling, we confirm its rarity, with a restricted potential occurrence equivalent to only 0.00005 % of South America, 0.0003 % of the Andes, and 0.0009 % of Colombia. We projected the future potential occurrence of M. coccinea and found that it can have a reduction of 43.49 % in the best-case scenario and 89.06 % in the worst-case scenario in 2100. We describe the flowering and fruiting phenologies and demonstrate that the precipitation two months before may determine the first one. Masdevallia coccinea is a rewardless species and, unlike most Pleurothallidinae species, we show that it is self-compatible but non-autonomous selfer. Thus, it is dependent on biotic pollination, performed only by Leucophenga sp. (Drosophilidae: Diptera) which has low efficiency (8.6 % of fruit set). This is the first pollinator report for the genus. While self-compatibility may be related to reproductive assurance, apparently inbreeding depression may affect populations since selfed fruits had less viable seeds. Nevertheless, self-pollination can be avoided by the retention of the anther cap on pollinia, giving more time until the pollinator flies away to another flower. We consider that the rarity of M. coccinea may be a result of both anthropogenic (habitat loss, climate change, and overcollection) and natural factors (high elevation distribution, self-compatibility, rewardless strategy, pollinator specificity, and low fruit set). The several new facets investigated here can be used for future conservation strategies of this emblematic species as well as other high Andean threatened species.     

Differential effects of emergent Nothofagus dombeyi on growth and basal area of canopy species in an old‐growth temperate rainforest

Question: Does overyielding of tree species mixtures in vertically stratified forests depend on complementary light use? Location: Andes of south‐central Chile. Methods: Basal area data were obtained from 80 circular plots distributed regularly throughout old‐growth stands with an emergent Nothofagus dombeyi tier over a canopy composed mainly of Laureliopsis philippiana and Saxegothaea conspicua. Radial growth was measured from cores obtained from trees at the centre of each plot. The effects of competition on growth were evaluated through a competition index (CI) based on distances to and diameters of the two nearest neighbours. Results: Overall, basal area of the canopy species was only weakly affected by the number of N. dombeyi per plot, and with basal area of N. dombeyi. However, the two main canopy species responded differently: whereas basal area of S. conspicua was negatively correlated with that of N. dombeyi, that of L. philippiana showed no response. Radial growth of S. conspicua was negatively correlated with CI calculated from canopy trees and more weakly so from emergent N. dombeyi. In contrast, radial growth of L. philippiana was not affected by competition with either canopy or emergent neighbours. Conclusions: Results indicate that emergent N. dombeyi tend to depress growth and basal area of S. conspicua, but not of the more shade‐tolerant L. philippiana. This supports the proposal that enhancement of wood production in stratified mixtures will be greatest when component species have strongly contrasting light use traits.     

Multilocus coalescent analysis of haemoglobin differentiation between low- and high-altitude populations of crested ducks (Lophonetta specularioides)

Hypoxia is a key factor determining survival, and haemoglobins are targets of selection in species native to high-altitude regions. We studied population genetic structure and evaluated evidence for local adaptation in the crested duck (Lophonetta specularioides). Differentiation, gene flow and time since divergence between highland and lowland populations were assessed for three haemoglobin genes (α(A) , α(D) , β(A) ) and compared to seven reference loci (six autosomal introns and mtDNA). Four derived amino acid replacements were found in the globin genes that had elevated Φ(ST) values between the Andean highlands and Patagonian lowlands. A single β(A) -globin polymorphism at a site known to influence O(2) affinity was fixed for different alleles in the two populations, whereas three α(A) - and α(D) -globin polymorphisms exhibited high heterozygosity in the highlands but not in the lowlands. Coalescent analyses supported restricted gene flow for haemoglobin alleles and mitochondrial DNA but nonzero gene flow for the introns. Simulating genetic data under a drift-migration model of selective neutrality, the β(A) -globin fell outside the 95% confidence limit of simulated data, suggesting that directional selection is maintaining different variants in the contrasting elevational environments, thereby restricting migration of β(A) -globin alleles. The α(A) - and α(D) -globins, by contrast, did not differ from the simulated values, suggesting that variants in these genes are either selectively neutral, or that the effects of selection could not be differentiated from background levels of population structure and linkage disequilibrium. This study illustrates the combined effects of selection and population history on inferring levels of population divergence for a species distributed across an altitudinal gradient in which selection for hypoxia resistance has likely played an important role.     

Dimensions of health and social structure in the early intermediate period cemetery at Villa El Salvador, Peru

This paper examines relationships between the social structure of a community and the health of its members, based on analysis of human skeletal remains (N = 64) from Villa El Salvador XII (100 BC-AD 100), a prehistoric cemetery located in the lower Lurín Valley, Peru. The ambiguity of social status as conventionally inferred from archaeological context is among the principal complicating factors in such an inquiry. We use multidimensional scaling of skeletal markers to identify the presence of patterned health-based heterogeneity in our sample, without making a priori assumptions about underlying social structure at Villa El Salvador. This procedure situates every skeleton relative to all others in the sample on the basis of multiple health markers, eliciting health groups. Once recognized, the relevance of those groups to social structure can be evaluated by comparison with a broad range of presumptive archaeological status indicators. We test the hypothesis that the distribution of stress indicators in human skeletons covaries with archaeological indicators of social differentiation. Based on multivariate analysis of skeletal indicators, we conclude that the cemetery at Villa El Salvador was utilized by two social groups with different geographic affinities: one of local coastal origin, and the other probably from the upper Lurín Valley or adjacent higher altitudes. These groups differ in skeletal characteristics related to childhood health, probably reflecting systematic contrasts in the growth environments of the studied individuals. This same division is independently supported by the distribution of cranial deformation, a possible marker of ethnicity. We also document some inequality in the distribution of labor among male individuals, as reflected by the relative advancement of degenerative joint disease, and congruent with differences in the number and quality of associated funerary offerings.     

Interpersonal violence in prehistoric San Pedro de Atacama, Chile: behavioral implications of environmental stress

The prehistoric population of San Pedro de Atacama lived through periods marked by prosperity and interregional interaction, as well as times of severe drought, social stress, and widespread poverty. A sample of 682 crania was analyzed for evidence of cranial trauma in order to assess changing patterns of interpersonal violence during the occupation of the oasis. It was hypothesized that the level of traumatic injuries in this population would parallel some of the changes seen in the archaeological record. Low fracture rates would be expected in periods of affluence and environmental stability, while periods characterized by environmental extremes and state collapse would yield elevated rates of aggression. This analysis found that rates of trauma escalated from 5.1% (5/99) in the earliest period, to 10.9% (10/92) in the Middle Horizon (AD 600-950). Although it may reflect problems related to increasing population density in the oasis, this increase is surprising, given that the early period witnessed the shift to permanent settlements, and the middle period was one of prosperity and plentiful resource availability. Trauma rates peaked at 35.6% (16/45) in an early Late Intermediate period (AD 950-1400) cemetery, with other Late Intermediate cemeteries demonstrating similarly high rates of traumatic injury. The elevated trauma rates during this period correlate with major droughts, the concentration of settlements on the oasis' east side, fortified structures, and material poverty, all reflected in the archaeological record. As the Late Intermediate waned and environmental conditions improved, trauma concomitantly decreased (7.0%), and remained low throughout the Inka occupation (AD 1400-1532). This indicates that while the Atacama was not peaceful, violence became commonplace only during periods of great social change and resource stress.     

Integrative taxonomy reveals cryptic Amazonian species of Pristimantis (Anura: Strabomantidae)

Hypotheses on the taxonomic status of two Bolivian Pristimantis with taxonomic problems are assessed by an integrative taxonomic approach that integrates three independent lines of evidence: external morphology, prezygotic reproductive barriers (advertisement calls) and reciprocal monophyly (phylogenetic analyses of partial 16S mtDNA sequences). Central Andean Bolivian populations previously assigned to either P. peruvianus or P. dundeei, and lowland Amazonian populations from southern Peru and northern Bolivia previously considered P. peruvianus do not correspond to these species. Indeed, multivariate analyses of qualitative and quantitative morphological and bioacoustic characters, and phylogenetic analyses support the hypothesis that they represent different, previously unknown, cryptic lineages. They are herein described as new species. The former is a sibling species of P. fenestratus that inhabits the Amazonian and semideciduous forests of the Andean foothills in central Bolivia. The latter is sibling to the Andean species P. danae and is parapatric to it in the Amazonian lowland forests and adjacent foothills of northern Bolivia, southern Peru and adjacent Brazil. Most species of Neotropical frogs, and especially Pristimantis, have been described by using external qualitative morphological characters only. An extended integrative taxonomic approach, as exemplified herein, may lead to the discovery of many other cryptic and sibling lineages that would increase the species numbers of tropical areas. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 97–122.     

Nest orientation of the Spotted Barbtail, <Emphasis Type="Italic">Premnoplex brunnescens</Emphasis>, is strongly correlated with stream flow

The placement and orientation of bird nests may strongly influence reproductive success. For many species, nest orientation is related to the cardinal directions and has to do with prevailing winds or solar exposure. Nest orientation differs among species in different environments, variously cooling or warming nests to maintain a nest microclimate optimal for successful development of eggs and young. The Spotted Barbtail (Premnoplex brunnescens) builds mossy, enclosed nests along shaded streams in Neotropical cloud forests. It shows a unique pattern of nest orientation, whereby nests are oriented in relation to the direction of water flowing below the nest entrance, rather than compass bearing. Nests face in one of three directions in relation to the stream: downstream, upstream, or perpendicular to the flow of the water. I discuss the ability of various hypotheses to explain this pattern in the context of factors affecting nest orientation in other species. While the reasons for this pattern of orientation remain unclear, orientation is likely driven by the need to create and maintain an optimal internal nest microclimate.