Population demography influences climatic niche evolution: evidence from diploid American Hordeum species (Poaceae)

In this study, we explore the interplay of population demography with the evolution of ecological niches during or after speciation in Hordeum. While large populations maintain a high level of standing genetic diversity, gene flow and recombination buffers against fast alterations in ecological adaptation. Small populations harbour lower allele diversity but can more easily shift to new niches if they initially survive under changed conditions. Thus, large populations should be more conservative regarding niche changes in comparison to small populations. We used environmental niche modelling together with phylogenetic, phylogeographic and population genetic analyses to infer the correlation of population demography with changes in ecological niche dimensions in 12 diploid Hordeum species from the New World, forming four monophyletic groups. Our analyses found both shifts and conservatism in distinct niche dimensions within and among clades. Speciation due to vicariance resulted in three species with no pronounced climate niche differences, while species originating due to long‐distance dispersals or otherwise encountering genetic bottlenecks mostly revealed climate niche shifts. Niche convergence among clades indicates a niche‐filling pattern during the last 2 million years in South American Hordeum. We provide evidence that species, which did not encounter population reductions mainly showed ecoclimatic niche conservatism, while major niche shifts occurred in species which have undergone population bottlenecks. Our data allow the conclusion that population demography influences adaptation and niche shifts or conservatism in South American Hordeum species.     

An energy balance from absorbed photons to new biomass for Chlamydomonas reinhardtii and Chlamydomonas acidophila under neutral and extremely acidic growth conditions

Chlamydomonas is one of the most well-studied photosynthetic organisms that had important biotechnological potential for future bioproductions of biofuels. However, an energy balance from incident photons to the energy stored in the new biomass is still lacking. In this study, we applied a recently developed system to measure the energy balance for steady state growth of Chlamydomonas reinhardtii grown at pH 6.5, and C. acidophila that was grown at pH 6.5 and 2.6. Energy use efficiency was quantified on the basis of light absorption, photosynthetic quantum yield, photosynthetic and respiratory quotient, and electron partitioning into proteins, carbohydrates and lipids. The results showed that lower growth rates of C. acidophila under both pH conditions were not caused by the differences in the photosynthetic quantum yield or in alternative electron cycling, but rather by differences in the efficiency of light absorption and increased dark respiration. Analysis of the macromolecular composition of the cells during the light phase showed that C. acidophila uses biosynthetic electrons preferentially for carbohydrate synthesis but not for synthesis of lipids. This led to a strong diurnal cycle of the C/N ratio and could explain the higher dark respiration of C. acidophila compared with C. reinhardtii .     

Machaeridian locomotion

The discovery that machaeridians (class Machaeridia Withers, 1926) are annelids allows their mode of locomotion to be interpreted in the context of the body plan of this phylum. The Plumulitidae were errant epibenthic forms, moving with parapodia. The body of Turrilepadidae and Lepidocoleidae, however, was enclosed largely within the mineralized plates that make up the skeleton. Articulated specimens indicate that these machaeridians were able to burrow like other annelids using peristaltic locomotion. A lepidocoleid specimen indicates that multiple waves of shortened and contracted regions moved over the body. This is in contrast to the mode of locomotion in earthworms and most polychaetes, but similar to peristaltic progression in Polyphysia (Scalibregmidae). Either the rugose sculpture (turrilepadids) and/or the margins of the overlapping shell plates functioned as a burrowing sculpture, allowing forward movement but preventing backwards slipping. A trace from the Devonian Hunsrück Slate associated with a lepidocoleid indicates that considerable flexing of the skeleton was possible, but this is an escape trace and does not represent normal locomotion. Features of the skeleton of machaeridians are convergent on those of molluscs where the shells likewise function in protection and burrowing.     

Diversity, evolutionary specialization and geographic distribution of a mutualistic ant-plant complex: Macaranga and Crematogaster in South East Asia

The most conspicuous and species-rich ant-plant mutualism in the Malesian region is found in the important pioneer tree genus Macaranga , yet little is known about the identities or community ecology of the species involved. Our studies have revealed a far more complex system than previously thought. This paper presents the first extensive investigation in the whole distribution area of myrmecophytic Macaranga. All ant-inhabited species were restricted to the moister parts of SE Asia: Peninsular Malaysia, South and East Thailand, Sumatra and Borneo. We found a rather strict and similar altitudinal zonation of myrmecophytic Macaranga species in all regions. Here we focus on the majority of the 19 Macaranga species obligatorily associated with ants of the genus Crematogaster. We identified a total of 2163 ant queens which belonged to at least eight (morpho)species of the small subgenus Decacrema as well as to one non-Decacrema (probably from Atopogyne ). The ant species were not randomly distributed among the Macaranga species but distinct patterns of associations emerged. Despite common sympatric distribution of Macaranga species, in most cases a surprisingly high specificity of ant colonization was maintained which was, however, often not species-specific but groups of certain plant species with identical ant partners could be found. These colonization patterns usually but not always mirror existing taxonomic sections within the genus Macaranga. Possible mechanisms of specificity are discussed. The results are compared with other ant-plant mutualisms.     

Potential for passive internal dispersal: eggs of an aquatic leaf beetle survive passage through the digestive system of mallards

相似文献   

Evidence for mate‐encounter Allee effect in an invasive longhorn beetle (Coleoptera: Cerambycidae)

1. Limited empirical support is available for mate‐encounter Allee effects in invasive insects due to the logistical challenges of studying demographic trends in low‐density populations. 2. Traps baited with pheromone and spruce volatiles were used to monitor the abundance of female Tetropium fuscum F. (Coleoptera: Cerambycidae) at multiple sites in Nova Scotia in 2011 and 2012. Each female was dissected to determine the presence or absence of sperm in its spermatheca (mated or virgin female, respectively). 3. Both male and total T. fuscum abundance declined with increasing distance to the focal point of T. fuscum's invasion. Female mating probability declined with male abundance and with distance from the invasion focus, and mating probabilities were very low at the most peripheral sites. Difficulty in encountering mates may thus contribute to limiting the spread of T. fuscum. 4. The approach outlined here could be integrated into existing surveys of wood borers using traps baited with semiochemicals to improve our understanding of the role of the mate‐encounter Allee effect in invasion dynamics.     

Are altitudinal limits of equatorial stream insects reflected in their respiratory performance?

1. We measured respiration of the larvae of aquatic insects from streams in the Ecuadorian Andes in relation to oxygen saturation at 5, 8, 11, 14 and 17 °C. Polycentropus (Polycentropodidae), Lachlania (Oligoneuriidae), Anchytarsus (Ptilodactylidae) and Anacroneuria (Perlidae) represented genera absent from the highest altitudes, reaching 2720, 2930, 3120, 3450 m a.s.l., respectively, while Claudioperla (Gripopterygidae) and Anomalocosmoecus (Limnephilidae) occurred only above 2900 m a.s.l. Our purpose was to determine whether natural altitudinal limits were reflected in physiological critical points on respiration versus oxygen curves and by the effect of temperature on the ability to oxy‐regulate. 2. For all six genera, respiration was affected by oxygen saturation and temperature. Respiration (mg O₂ g⁻¹ AFDM h⁻¹) at 70% oxygen saturation (Michaelis–Menten fitted) varied from 2.6 to 7.6 between genera at 17 °C, and from 1.3 to 2.5 at 5 °C. Q₁₀ values for this temperature interval ranged 1.5–2.9 (mean 2.3). The two “high‐altitude” genera had higher respiration rates at low temperature and oxygen saturation, and their respiration rate saturated at lower temperatures, than three of the four “low‐altitude” genera. 3. The oxy‐regulatory capacity (critical points and initial decrease in respiration versus oxygen regressions) varied among genera and was affected by temperature. Lachlania, Claudioperla and Anomalocosmoecus had a higher ability to oxy‐regulate at low than at high temperatures, Anacroneuria was not clearly affected by temperature, while Polycentropus and Anchytarsus had a greater oxy‐regulatory capacity at high than at low temperature. These results indicate that the ability to oxy‐regulate is related to the temperature (altitude) at which species naturally occur. 4. Upper altitudinal limits of the six genera were not reflected in their respiratory performance, because all genera had critical minima of temperature and oxygen saturation much lower than those occurring at the limits of their natural distribution. So, the altitudinal limit could not be attributed to absolute short‐term physiological tolerance of low temperature and oxygen concentration. 5. Multiple regressions (based on respiration experiments and previously obtained relationships between water temperature, oxygen saturation and altitude) were used to predict how respiration rates should vary with altitude. At the upper limit of the four “low‐altitude” genera, respiration rates were 50–68% of those predicted at the centre of the range. With an arbitrary increase of 400 m above the actual limit, the effect of temperature would be a 13% decrease, and that of oxygen a 2% decrease, in respiration rate of Polycentropus, Lachlania and Anacroneuria, while respiration in Anchytarsus would be reduced by 5% by both factors. 6. It seems that, while the immediate decrease in respiration with increased altitude is caused mainly by a decrease in temperature, the long‐term survival of a species at given altitudes might be more affected by oxygen saturation. Further quantitative and long‐term studies on survival and recruitment in populations and communities are needed to determine the importance of temperature and oxygen for altitudinal limits of aquatic insects.     

Genital morphology and taxonomy of the water strider Aquarius remigis (Say) (Insecta, Hemiptera-Heteroptera: Gerridae)

The shape of the dorsal vesical plate was used to determine the extent of morphological differentiation among populations of the water strider Aquarius remigis (Say) (Hemiptera-Heteroptera: Gerridae), and between species assigned to the A. remigis species group. Populations were sampled throughout North America and Mesoamerica, and included paratypes of A. remigoides Gallant & Fairbairn, and material collected from the type localities of A. amplus (Drake & Harris) and A. nyctalis (Drake & Hottes). If taxonomy is to be inferred from the shape of the dorsal vesical plate, as suggested by previous authors, several taxonomic issues need to be reconsidered. First, there was one species distributed widely across North America and deep into Mexico that is very likely to represent A. remigis , meaning that populations from the western USA previously assigned to ' A. nyctalis ' should be synonymized with this species. Second, A. remigoides as currently defined also includes some populations of A. remigis , and is probably much less widely distributed in the south-eastern USA than previously thought. A hybridization zone in Pennsylvania between A. remigis and A. remigoides , as inferred from measurements of body size and allozyme electrophoresis, is not congruent with data from the male genitalia, which indicated a transition zone between the two forms in Virginia much further to the south. Finally, A. amplus was widespread in Mexico, reaching into Guatemala to the south and into Arizona to the north.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 381–398.     

How much genetic variation in fern populations is stored in the spore banks? A study of Athyrium filix-femina (L.) Roth

The genetic variation within spore banks of Athyrium filix-femina (L.) Roth from three sites in north-eastern Switzerland was investigated. At two sites spore banks were located beneath sporophyte populations. One collection site was 10Om away from a sporophyte population. The gametophytes grown from the soil samples, the dimensions of which were 4 × 4 × 1.5 cm, and sporophytes from each site were analysed electrophoretically for either three or four variable allozyme loci. The spore banks from the different soil samples within and between populations revealed a considerable amount of genetic diversity. The most frequent alleles within the two sporophyte populations were, with a few exceptions, also the most frequent within the spore banks. The influence of single sporophytic individuals on the genetic composition of microsites seems to be considerably reduced by stochastic processes such as soil movement or the action of earthworms, which promote the mixing of spores from different spatial and temporal origins. It was shown that spores remain viable after passing through the gut of earthworms and that spore banks from even small soil samples revealed genetic diversity and could lead to a large number of genetically distinct sporophytes. The results suggest that fertilization seems to be close to random because the sporophyte populations sampled were in Hardy-Weinberg equilibrium and had fixation index ( F _is) close to zero.     

Immigration and in situ glacial survival of the low-alpine Erinus alpinus (Scrophulariaceae)

It has been hypothesized that the subalpine Erinus alpinus survived the Pleistocene glaciation in southern French refugia peripheral to the Alps and postglacially immigrated to its northern Alpine distribution (tabula rasa hypothesis). However, E. alpinus is also known from nunataks in the northern Prealps. PCR–RFLP of the cpDNA revealed no variation, whereas AFLPs identified three phylogeographical groups among the 22 populations: (1) a central Swiss group, (2) a single central Swiss population on Mount Rigi, and (3) all other populations located to the west and east of the central Swiss group (west-eastern populations). The population representing the putative French refugium was not distinct from the west-eastern populations but was different from the populations of central Switzerland. We consider this support for locally restricted in situ survival of E. alpinus in the northern Prealps or nearby Jura mountains (dating back to 60–28 ky BP). However, the west-eastern gene-pool probably immigrated postglacially from southern France through the prealpine lowlands (not before 14.6 kyr BP), skirting central Switzerland. The near-absence of gene flow among the central Swiss and the west-eastern populations may be the reason why these historical genetic patterns are still detectable.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77, 87–103.