On the evolutionary stability of sink populations

The evolution of adaptive behaviours can influence population dynamics. Conversely, population dynamics can affect both the rate and direction of adaptive evolution. This paper examines reasons why sink populations – populations maintained by immigration, preventing local extinction – might persist in the habitat repertoire of a species over evolutionary time-scales. Two such reasons correspond to standard explanations for deviations from an ideal free habitat distribution: organisms may not be free to settle in whichever habitat has the highest potential fitness, and may be constrained by costs, perceptual limitations, or mode of dispersal in the acuity of their habitat selectivity. Here, I argue that a third general reason for persistent sink populations is provided by unstable population dynamics in source habitats. I present a simple model illustrating how use of a sink habitat may be selectively advantageous, when a source population has unstable dynamics (which necessarily reflects temporal variation in local fitnesses). Species with unstable local dynamics in high-quality habitats should be selected to utilize a broader range of habitats than species with stable local dynamics, and in particular in some circumstances should utilize sink habitats. This observation has implications for the direction of niche evolution, and the likelihood of niche conservatism.     

The phylogenetic signal of diversification rates

Hypotheses to explain the causes of diversity gradients have increasingly focused on the factors that actually change species numbers, namely speciation, extinction and dispersal. A common assumption of many of these hypotheses is that there should be phylogenetic signal in diversification rates, yet this assumption has rarely been tested explicitly. In this study, we compile a large data set including 328,219 species of plants, mammals, amphibians and squamates to assess the level of phylogenetic signal in their diversification rates. Significant phylogenetic signal was detected in all data sets, except for squamates, suggesting not only that closely related clades indeed might share similar diversification rates, but also that the level of phylogenetic signal might vary considerably between them. Moreover, there were intriguing differences among taxa in the rate of decay in phylogenetic autocorrelation over time, underscoring the existence of taxon-specific patterns of phylogenetic autocorrelation. These results have important implications for the development of more realistic models of species diversification.     

Genetic diversity and ecological niche modelling of the restricted Recordia reitzii (Verbenaceae) from southern Brazilian Atlantic forest

Genetic diversity analyses, coupled with ecological niche modelling (ENM) of species with a restricted distribution, may provide valuable information for understanding diversification patterns in endangered areas. We analyzed the genetic diversity of Recordia reitzii, a tree restricted to the threatened and highly fragmented Brazilian Atlantic forest, using three intergenic cpDNA spacers and ten microsatellite (SSR) loci. To assess the historical processes that may have influenced the distribution of extant R. reitzii populations, the current potential distributions of R. reitzii and Recordia boliviana, a closely related species, were modelled and projected onto the Last Glacial Maximum (LGM) and Last Interglacial (LIG) periods. Niche divergence was quantified between these two. The cpDNA and SSR data showed a north–south pattern of the diversity distribution and structured populations, suggesting that gene flow is probably limited. According to our data, R. reitzii exhibits low genetic diversity, which may be a result of a founder or distribution‐reduction effect, narrow distribution or small population size. The ecological niche models showed a wider palaeodistribution during the LIG and a retraction during the LGM for both species. Tests of niche divergence and conservatism indicated that bioclimatic factors might have influenced the diversification of these Recordia species. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 332–348.     

Evolutionary relationships of Pemphigus and allied genera （Hemiptera： Aphididae： Eriosomatinae） and their primary endosymbiont,Buchnera aphidicola

Aphids harbor primary endosymbionts, Buchnera aphidicola, in specialized cells within their body cavities. Aphids and Buchnera have strict mutualistic relationships in nutrition exchange. This ancient association has received much attention from researchers who are interested in endosymbiotic evolution. Previous studies have foundparallel phylogenetic relationships between non-galling aphids and Buchnera at lower taxonomic levels （genus, species）. To understand whether relatively isolated habitats such as galls have effect on the parallel relationships between aphids and Buchnera, the present paper investigated the phylogenetic relationships of gall aphids from Pemphigus and allied genera, which induce pseudo-galls or galls on Populus spp. （poplar） and Buchnera. The molecular phylogenies inferred from three aphid genes （COI, COII and EF-la） andtwo Buchnera genes （gnd, 16S rRNA gene） indicated significant congruence between aphids and Buchnera at generic as well as interspecific levels. Interestingly, both aphid andBuchnera phylogenies supported three main clades corresponding to the galling locations of aphids, namely leaf, the joint of leaf blade and petiole, and branch of the host plant.The results suggest phylogenetic conservatism of gall characters, which indicates gall characters are more strongly affected by aphid phylogeny, rather than host plants.     

Phylogenetic niche conservatism, phylogenetic signal and the relationship between phylogenetic relatedness and ecological similarity among species

Ecologists are increasingly adopting an evolutionary perspective, and in recent years, the idea that closely related species are ecologically similar has become widespread. In this regard, phylogenetic signal must be distinguished from phylogenetic niche conservatism. Phylogenetic niche conservatism results when closely related species are more ecologically similar that would be expected based on their phylogenetic relationships; its occurrence suggests that some process is constraining divergence among closely related species. In contrast, phylogenetic signal refers to the situation in which ecological similarity between species is related to phylogenetic relatedness; this is the expected outcome of Brownian motion divergence and thus is necessary, but not sufficient, evidence for the existence of phylogenetic niche conservatism. Although many workers consider phylogenetic niche conservatism to be common, a review of case studies indicates that ecological and phylogenetic similarities often are not related. Consequently, ecologists should not assume that phylogenetic niche conservatism exists, but rather should empirically examine the extent to which it occurs.     

The role of ``conservatism' in herring migrations

Herring (Clupea harengus) migrationstend to remain constant over periods of severalyears or even decades, despite environmentalvariation. When a migration pattern is changed,apparently in response to an environmentalstimulus, the change in migratory behaviorsometimes lasts longer than the environmentalstimulus itself. This paper reviews evidencethat the response of herring to environmentalchange is restrained by conservatism. Herringapparently develop certain migratory habitsduring the early stage of adult life and tendto adhere to these habits for life, even whenthe environment changes. Two elements ofconservatism are distinguished: the formationof habits within one generation, and thetransfer of habits between generations. Anumber of case studies on North Sea herring andNorwegian spring spawning herring are reviewedin order to find evidence for habit formationand tradition in the migrations of thesepopulations. By eliminating the possibilitythat homing to spawning, wintering and feedinggrounds is due to innate behavior orenvironmental constraints, it is shown that thereturn of these fish to the same areas eachyear is most likely a form of learned behavior.In many cases, new year-classes adopt the samemigration pattern as their predecessors, whichis explained by the social transfer of habitsfrom old herring to young ones. A change ofmigration pattern is usually initiated by arecruiting year-class that lacks the ``guidance'of older herring at the time it has to startits first migration. This may be the effect ofa special environmental condition that affectsthe distribution of the recruiting age groupmore than that of the adult stock component, andthereby results in a separation of the twostock components. After the recruitingyear-class has adopted the new migration route,it tends to repeat it in subsequent years. Thenew migration thus becomes habitual. Subsequentgenerations may copy the migration and continuethis behavior even after the originalenvironmental cause has disappeared.     

Evolutionary relationships of Pemphigus and allied genera (Hemiptera: Aphididae: Eriosomatinae) and their primary endosymbiont,Buchnera aphidicola

Aphids harbor primary endosymbionts, Buchnera aphidicola, in specialized cells within their body cavities. Aphids and Buchnera have strict mutualistic relationships in nutrition exchange. This ancient association has received much attention from researchers who are interested in endosymbiotic evolution. Previous studies have found parallel phylogenetic relationships between non‐galling aphids and Buchnera at lower taxonomic levels (genus, species). To understand whether relatively isolated habitats such as galls have effect on the parallel relationships between aphids and Buchnera, the present paper investigated the phylogenetic relationships of gall aphids from Pemphigus and allied genera, which induce pseudo‐galls or galls on Populus spp. (poplar) and Buchnera. The molecular phylogenies inferred from three aphid genes (COI, COII and EF‐1α) and two Buchnera genes (gnd, 16S rRNA gene) indicated significant congruence between aphids and Buchnera at generic as well as interspecific levels. Interestingly, both aphid and Buchnera phylogenies supported three main clades corresponding to the galling locations of aphids, namely leaf, the joint of leaf blade and petiole, and branch of the host plant. The results suggest phylogenetic conservatism of gall characters, which indicates gall characters are more strongly affected by aphid phylogeny, rather than host plants.     

Multiregional comparison of the ecological and phylogenetic structure of butterfly species richness gradients

Aim To examine butterfly species richness gradients in seven regions/countries and to quantify geographic mean root distance (MRD) patterns. My primary goal is to determine the extent to which an explanation for butterfly richness patterns based on tropical niche conservatism and the evolution of cold tolerance, proposed for the fauna of Canada and the USA, applies to other parts of the world. Location USA/Canada, Mexico, Europe/NW Africa, Transbaikal Siberia, Chile, South Africa and Australia. Methods Digitized range maps for butterfly species in each region were used to map richness patterns in summer (for all areas) and winter (for USA/Canada, Europe/NW Africa and Australia). A phylogeny resolved to subfamily was used to map the geographic MRD patterns. Regression trees and general linear models examined climatic and vegetation correlates of species richness and MRD within and among regions. Results Various combinations of climate and vegetation were strong predictors of species richness gradients within regions, but unresolved ‘regional’ factors contributed to the multiregional pattern. Regionally based differences in phylogenetic structure also exist, but MRD is negatively correlated with temperature both within and across areas. MRD patterns consistent with tropical niche conservatism occur in most areas. With a possible partial exception of Mexico, faunas in cold climates and in mountains are more derived than faunas in lowlands and tropical/subtropical climates. In USA/Canada, Europe and Australia, winter faunas are more derived than summer faunas. Main conclusions The phylogenetic pattern previously found in the USA and Canada is widespread in both the Northern and Southern Hemispheres, and niche conservatism and the evolution of cold tolerance is the likely explanation for the development of the global butterfly species richness gradient over evolutionary time. Contemporary climate also influences species richness patterns but is unlikely to be a complete explanation globally. The importance of climate is also manifested in the seasonal loss of more basal butterfly elements outside the tropics in winter.     

Intra‐ and interspecific differences in nutrient recycling by European freshwater fish

1. We measured N and P excretion rates of 470 individuals belonging to 18 freshwater fish species widespread in Western Europe. We assessed the effect of body mass on excretion rates at both the intra‐ and interspecific levels. 2. The high variability in per capita N and P excretion rates was mainly determined by differences in body mass. The scaling coefficients of allometric relationships for both N and P excretion rates were significantly lower than 1 (mean ± SE, 0.95 ± 0.04 and 0.81 ± 0.05, respectively). 3. The slope of the allometric relationship between fish mass and nutrient excretion rate was significantly different among species. We did not detect any influence of phylogenetic conservatism on fish mass and on excretion rates. Further investigations are needed to understand the biological determinants of these differences. 4. This high intra‐ and interspecific variability in per capita excretion rates, coupled with differences in fish body mass, produce marked differences in biomass‐standardised excretion rates. These results thus indicate the necessity for further experimental and in situ investigations on the consequences of nutrient recycling by fish in freshwater ecosystems.     

Different evolutionary histories underlie congruent species richness gradients of birds and mammals

Aim The global species richness patterns of birds and mammals are strongly congruent. This could reflect similar evolutionary responses to the Earth’s history, shared responses to current climatic conditions, or both. We compare the geographical and phylogenetic structures of both richness gradients to evaluate these possibilities. Location Global. Methods Gridded bird and mammal distribution databases were used to compare their species richness gradients with the current environment. Phylogenetic trees (resolved to family for birds and to species for mammals) were used to examine underlying phylogenetic structures. Our first prediction is that both groups have responded to the same climatic gradients. Our phylogenetic predictions include: (1) that both groups have similar geographical patterns of mean root distance, a measure of the level of the evolutionary development of faunas, and, more directly, (2) that richness patterns of basal and derived clades will differ, with richness peaking in the tropics for basal clades and in the extra‐tropics for derived clades, and that this difference will hold for both birds and mammals. We also explore whether alternative taxonomic treatments for mammals can generate patterns matching those of birds. Results Both richness gradients are associated with the same current environmental gradients. In contrast, neither of our evolutionary predictions is met: the gradients have different phylogenetic structures, and the richness of birds in the lowland tropics is dominated by many basal species from many basal groups, whereas mammal richness is attributable to many species from both few basal groups and many derived groups. Phylogenetic incongruence is robust to taxonomic delineations for mammals. Main conclusions Contemporary climate can force multiple groups into similar diversity patterns even when evolutionary trajectories differ. Thus, as widely appreciated, our understanding of biodiversity must consider responses to both past and present climates, and our results are consistent with predictions that future climate change will cause major, correlated changes in patterns of diversity across multiple groups irrespective of their evolutionary histories.     

Patterns of hind limb motor output during walking in the salamander Dicamptodon tenebrosus,with comparisons to other tetrapods

Based on similarity of motor patterns of lizards, crocodiles, birds and mammals, various authors have concluded that a number of homologous muscles across these taxa demonstrate neuromuscular conservatism. This hypothesis remains untested for more basal taxa. Therefore, a quantitative electromyographic study of the hind limb during treadmill walking (mean speed of 0.75 SVL/s) in the salamander Dicamptodon tenebrosus was undertaken. Muscles located ventrally on the hind limb become active just before foot placement on the substrate, and maintain activity through the first half of the stance phase. Dorsally located muscles begin activity at or just before the start of the swing phase, and fire through the first half of swing. Several muscles showed a secondary EMG burst during the stride. The second burst in most ventral muscles occurred in late stance. In all dorsal muscles with double bursts, the second burst occurred in the middle of stance. Comparison of electromyographic onset and offset values for Dicamptodon to those for presumed homologues in other tetrapods reveals similarity in activity patterns for all ventral and two dorsal muscles despite anatomical rearrangements, supporting the hypothesis of neuromuscular conservatism for some muscles but not others.Abbreviations BF biceps femoris muscle - CDF caudofemoralis muscle - CPIT caudalipuboischiotibialis muscle - Dist distal - EDC extensor digitorum communis muscle - EMG electromyogram - EXF extensor cruris et tarsi fibularis muscle - EXT extensor cruris tibialis muscle - FMFB femorofibularis muscle - FPC flexor primordialis communis muscle - Gastroc gastrocnemius muscle - ILFB iliofibularis muscle - ILFM iliofemoralis muscle - ILTA extensor iliotibialis pars anterior muscle - ILTP extensor iliotibialis pars posterior muscle - ISC ischiocaudalis muscle - ISF ischioflexorius muscle - ISFM ischiofemoralis muscle - ITCR iliotrochantericus cranialis muscle - ITM iliotrochantericus medius muscle - MG medial gastrocnemius muscle - PFM pubifemoralis muscle - PIFE puboischiofemoralis externus muscle - PIFI puboischiofemoralis internus muscle - PIT puboischiotibialis muscle - Prox proximal - PTB pubotibialis muscle - Sol soleus muscle - ST semitendinosus muscle - SVL snout-vent length     

Testing ecological explanations for biogeographic boundaries

Barriers to dispersal and resulting biogeographic boundaries are responsible for much of life's diversity. Distinguishing the contribution of ecological, historical, and stochastic processes to the origin and maintenance of biogeographic boundaries, however, is a longstanding challenge. Taking advantage of newly available data and methods--including environmental niche models and associated comparative metrics--we develop a framework to test two possible ecological explanations for biogeographic boundaries: (1) sharp environmental gradients and (2) ribbons of unsuitable habitat dividing two highly suitable regions. We test each of these hypotheses against the null expectation that environmental variation across a given boundary is no greater than expected by chance. We apply this framework to a pair of Hispaniolan Anolis lizards (A. chlorocyanus and A. coelestinus) distributed on the either side of this island's most important biogeographic boundary. Integrating our results with historical biogeographic analysis, we find that a ribbon of particularly unsuitable habitat is acting to maintain a boundary between species that initially diverged on distinct paleo-islands, which merged to form present-day Hispaniola in the Miocene.     

Species' diversity in the New Caledonian endemic genera Cephalidiosus and Nobarnus (Insecta: Heteroptera: Tingidae), an approach using phylogeny and species' distribution modelling

The patterns of local endemism in New Caledonia were analysed in two endemic genera of Tingidae (Insecta, Heteroptera), Cephalidiosus and Nobarnus , through a phylogenetic analysis and species' distribution modelling. The aim was to determine the possible causes of diversification and endemism in New Caledonia. Our results show that environmental conditions are probably important for the distribution of the genus Cephalidiosus , in conjunction with other factors such as resource (host plant) distribution, but suggest that the same environmental conditions have not influenced the speciation processes and diversification in the genus.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 177–184.     

The effect of metapopulation dynamics on the survival and spread of a novel, conspicuous prey

Animals that deploy chemical defences against predators often signal their unprofitability using bright colouration. This pairing of toxicity and conspicuous patterning is known as aposematism.Explaining the evolution and spread of aposematic traits in previously cryptic species has been the focus of much empirical and theoretical work over the last two decades. Existing research concerning the initial evolution of aposematism does not however properly consider that many aposematic species (such as members of the hymenoptera, the lepidoptera, and amphibia) are highly mobile. We argue in this paper that the evolution of aposematic displays is therefore often best understood within a metapopulation framework; hence in this paper we present the first explicit metapopulation model of the evolution of aposematism. Our most general finding is that migration tends to reduce the probability that an aposematic prey can increase from rarity and spread across a large population. Hence, the best case scenarios for the spread of aposematism required fixation of the aposematic form in one or more isolated sub-habitats prior to some event which subsequently enabled migration. We observed that changes in frequency of new aposematic forms within source habitats are likely to be nonmonotonic. First, aposematic prey tend to decline in frequency as they migrate outwards from the source habitat to neighbouring sink habitats, but subsequently they increase in relative abundance in the source, as the descendents of earlier migrants migrate back from newly converted sub-populations. This pattern of initial loss and subsequent gain between new source and neighbouring sink habitats is then repeated as the aposematic form spreads via a moving cline.     

Evolutionary constraints on regional faunas: whom, but not how many

The latitudinal diversity gradient has been hypothesized to reflect past evolutionary dynamics driven by climatic niche conservation during cladogenesis, i.e. the tropical conservatism hypothesis. Here we show that the species diversity of treefrogs (Hylidae) across the western hemisphere is actually independent of evolutionary niche dynamics. We evaluated three key predictions of the tropical conservatism hypothesis that relate to the relationships between climate, species richness and the phylogenetic structure of regional treefrog faunas across the continental Americas. Species composition was dependent on the inability of some lineages to evolve cold tolerance, but the actual number of species in a region was strongly predicted by precipitation, not temperature. Moreover, phylogenetic structure was independent of precipitation. Thus, species in low-richness areas were no more closely related than species in highly diverse regions. These results provide no support for the tropical conservatism hypothesis. Instead, they show that regional species composition and richness are constrained by different climatic components, demonstrating that global biodiversity gradients can be independent of niche stasis during cladogenesis.