Functional coupling constrains craniofacial diversification in Lake Tanganyika cichlids

Functional coupling, where a single morphological trait performs multiple functions, is a universal feature of organismal design. Theory suggests that functional coupling may constrain the rate of phenotypic evolution, yet empirical tests of this hypothesis are rare. In fish, the evolutionary transition from guarding the eggs on a sandy/rocky substrate (i.e. substrate guarding) to mouthbrooding introduces a novel function to the craniofacial system and offers an ideal opportunity to test the functional coupling hypothesis. Using a combination of geometric morphometrics and a recently developed phylogenetic comparative method, we found that head morphology evolution was 43% faster in substrate guarding species than in mouthbrooding species. Furthermore, for species in which females were solely responsible for mouthbrooding the males had a higher rate of head morphology evolution than in those with bi-parental mouthbrooding. Our results support the hypothesis that adaptations resulting in functional coupling constrain phenotypic evolution.     

Functional diversification of kir7.1 in cichlids accelerated by gene duplication

Mutation in the inward rectifier potassium channel gene, kir7.1, was previously identified as being responsible for the broader stripe zebrafish skin pattern mutant, jaguar/obelix. An amino acid substitution in this channel causes a broader stripe pattern than that of wild type zebrafish. In this study we analyzed cichlid homologs of the zebrafish kir7.1 gene. We identified two kinds of homologous genes in cichlids and named them cikir7.1 and cikir7.2. Southern hybridization using cichlid genome revealed that cichlids from the African Great Lakes, South America and Madagascar have two copies of the gene. Cichlids from Sri Lanka, however, showed only one band in this experiment. Database analysis revealed that only one copy of the kir7.1 gene exists in the genomes of the teleosts zebrafish, tetraodon, takifugu, medaka and stickleback. The deduced amino acid sequence of cikir7.1 is highly conserved among African cichlids, whereas that of cikir7.2 has several amino acid substitutions even in conserved transmembrane domains. Gene expression analysis revealed that cikir7.1 is expressed specifically in brain and eye, and cikir7.2 in testis and ovary; zebrafish kir7.1, however, is expressed in brain, eye, skin, caudal fin, testis and ovary. These results suggest that gene duplication of the cichlid kir7.1 occurred in a common ancestor of the family Cichlidae, that the function of parental kir7.1 was then divided into two genes, cikir7.1 and cikir7.2, and that the evolutionary rate of cikir7.2 might have been accelerated, thereby effecting functional diversification in the cichlid lineage. Thus, the evolution of kir7.1 genes in cichlids provides a typical example of gene duplication--one gene is conserved while the other becomes specialized for a novel function.     

Density-dependent diversification in North American wood warblers

Evidence from both molecular phylogenies and the fossil record suggests that rates of species diversification often decline through time during evolutionary radiations. One proposed explanation for this pattern is ecological opportunity, whereby an initial abundance of resources and lack of potential competitors facilitate rapid diversification. This model predicts density-dependent declines in diversification rates, but has not been formally tested in any species-level radiation. Here we develop a new conceptual framework that distinguishes density dependence from alternative processes that also produce temporally declining diversification, and we demonstrate this approach using a new phylogeny of North American Dendroica wood warblers. We show that explosive lineage accumulation early in the history of this avian radiation is best explained by a density-dependent diversification process. Our results suggest that the tempo of wood warbler diversification was mediated by ecological interactions among species and that lineage and ecological diversification in this group are coupled, as predicted under the ecological opportunity model.     

Allopatric speciation in the desert: diversification of cichlids at their geographical and ecological range limit in Iran

Collated electrofishing data from wadeable riffles of boreal rivers in Finland revealed a substantial shift in the fish assemblage composition, accompanied by a decline in total fish density and a reduction in species richness from early summer to late autumn. As the major changes in fish assemblages, the density of cyprinids decreased sharply from June towards autumn, whereas salmonids peaked in September. These shifts were considered to originate mainly from spawning migrations, fish movements to winter refuge habitat and other temperature-related responses of rheophilic versus eurytopic fish species. Temporal change in fish assemblages induced a prominent variation in the monthly fish-based index values used for bioassessment. The proportion of sampled sites classified as high or good in ecological status within the Water Framework Directive (WFD) based on fish increased from 25.9% in July to 68.3% in October. These results, combined with the observed timing of young of the year (0+) fish recruitment to electrofishing catch, suggest that sampling of fish in boreal rivers for WFD monitoring should be restricted to a considerably shorter period than the prevailing practice in order to avoid temporal bias.     

Temporal diversification of Mesoamerican cichlid fishes across a major biogeographic boundary

The Mexican Neovolcanic Plateau sharply divides the vertebrate fauna of Mesoamerica where the climate of both the neotropics and temperate North America gradually blend. Only a few vertebrate groups such as the Heroine cichlids, distributed from South America to the Rio Grande in North America, are found both north and south of the Neovolcanic Plateau. To better understand the geography and temporal diversification of cichlids at this geologic boundary, we used mitochondrial DNA sequences of the cytochrome b (cyt b) gene to reconstruct the relationships of 52 of the approximately 80 species of Heroine cichlids in Mesoamerica. Our analysis suggests several cichlids in South America should be considered as part of the Mesoamerican Heroine clade because they and the cichlids north of the Isthmus of Panama are clearly supported as monophyletic with respect to all other Neotropical cichlids. We also recovered a group containing species in Paratheraps+Paraneetroplus+Vieja as the sister clade to Herichthys. Herichthys is the only cichlid clade north of the Mexican Plateau and it is monophyletic. Non-parametric rate smoothing of cichlid cyt b sequence resulted in an estimated divergence time of approximately 6 million years for Herichthys. This temporal diversification is concordant with divergence times estimated for anurans in the genus Bufo, a group that exhibits a similar geographic distribution. Our results indicate the 5-million-year-old extension of the Mexican Neovolcanic Plateau to the Gulf Coast of Mexico has strongly influenced the current transition between the vertebrate faunas of the Neotropics and Nearctic.     

Rapid diversification in the North American minnow genus Nocomis

Diversification rates among stream fishes are likely governed by geographical factors that impact connectivity among and between stream systems. Herein we investigate rates of diversification within species of River Chubs, Nocomis, a monophyletic group of stream fishes distributed throughout the drainage basins of the Mississippi River, Atlantic Slope and Gulf Coast. We used nucleotide sequences of two protein-coding nuclear genes (IRBP and rhodopsin) and one mitochondrial gene (cytochrome b) to generate a phylogenetic hypothesis of population-level relationships within and among species. Results of molecular analyses suggest that morphological and meristic treatments of Nocomis have underestimated species diversity within the group. Tree-based Bayesian methods and diversification statistics were implemented to model the rate of evolutionary change along lineages and estimate divergence dates among phylogroups. Significantly elevated rates of cladogenesis are observed among coastally distributed populations 2-3 million years before present. This period was dominated by dramatic sea level fluctuations that suggest a period of climatic instability. Climatic instability and other factors may have driven the burst of rapid diversification observed in Nocomis. Results generated in this study reinforce faunistic and geologic arguments for the hypothesized existence of extinct rivers, such as White's River and the Appalachian River.     

Temporal bird community dynamics are strongly affected by landscape fragmentation in a Central American tropical forest region

Habitat loss and fragmentation are considered the main causes of species extinctions, particularly in tropical ecosystems. The objective of this work was to evaluate the temporal dynamics of tropical bird communities in landscapes with different levels of fragmentation in eastern Guatemala. We evaluated five bird community dynamic parameters for forest specialists and generalists: (1) species extinction, (2) species turnover, (3) number of colonizing species, (4) relative species richness, and (5) a homogeneity index. For each of 24 landscapes, community dynamic parameters were estimated from bird point count data, for the 1998–1999 and 2008–2009 periods, accounting for species’ detection probability. Forest specialists had higher extinction rates and a smaller number of colonizing species in landscapes with higher fragmentation, thus having lower species richness in both time periods. Alternatively, forest generalists elicited a completely different pattern, showing a curvilinear association to forest fragmentation for most parameters. Thus, greater community dynamism for forest generalists was shown in landscapes with intermediate levels of fragmentation. Our study supports general theory regarding the expected negative effects of habitat loss and fragmentation on the temporal dynamics of biotic communities, particularly for forest specialists, providing strong evidence from understudied tropical bird communities.     

Observations on the biology of Rhabdochona kidderi texensis, a parasite of North American cichlids

An examination of a sample of benthic invertebrates collected from the Upper San Marcos River in southwestern Texas, USA in September 1999 revealed that the nymph of the ephemeropteran Tricorythodes curvatus served as natural intermediate host of the nematode Rhabdochona kidderi texensis (Nematoda: Rhabdochonidae), an intestinal parasite mainly of the Rio Grande perch (Cichlasoma cyanoguttatum) in this locality; the prevalence of the parasite's third- and fourth-stage larvae in mayflies was 6.8% with the intensity of 1-2 larvae per nymph. Live R. kidderi texensis eggs collected from nematodes recovered from C. cyanoguttatum in Texas were transported to the Czech Republic, where they were used to experimentally infect nymphs of the palaearctic mayfly species Paraleptophlebia submarginata; the development of infective third- and fourth-stage larvae in this experimental intermediate host was completed after approximately 10 days at 19 degrees C. Infected nymphs were fed to aquarium-reared fishes, four Cichlasoma nigrofasciatum and one Oreochromis niloticus, of which only three of the former became infected. The last (fourth) moult of a male nematode was observed in C. nigrofasciatum 23 days p.i. and adult males and gravid females with not fully mature (non-embryonated) eggs in uteri on days 40 and 51 p.i. The prepatent period of R. kidderi texensis is approximately two months.     

Feeding convergence in South American and African zooplanktivorous cichlids Geophagus brasiliensis and Tilapia rendalli

Synopsis Acará, Geophagus brasiliensis, and red-breasted bream, Tilapia rendalli, are important planktivorous cichlids in southern Brazilian lakes and reservoirs. In laboratory experiments, I quantified behavior and selectivity of different sizes of these two fish feeding on lake zooplankton. Feeding behavior depended on fish size. Fish < 30 mm were visual feeders. Fish 30–50 mm either visually fed or pump-filter fed depending on zooplankton size. Fish > 70 mm were pump-filter feeders. Replicate 1 h feeding trials revealed that, as the relative proportions of prey changed during an experiment, acará (30–42 mm, standard length) and tilapia (29–42 mm) shifted from visual feeding on large evasive copepods to filter feeding on small cladocerans and rotifers. Electivity and feeding rate increased with prey length, but were distinct for similar-sized cladocerans and copepods. Visual/filter-feeding fish had lowest electivities for small and poorly evasive rotifers and cyclopoid nauplii. They fed non-selectively on cyclopoid copepodites, had intermediate electivities for calanoid nauplii and small cladocerans, and had highest electivities for large cladocerans, cyclopoid adults, and calanoid copepodites and adults. Although belonging to different cichlid genera and native to South America and Africa, respectively, acará and red-breasted bream (= congo tilapia) exhibited similar selectivity for zooplankton. Apparently, few stereotyped feeding behaviors have evolved during the acquisition of microphagy in fish. Shift in feeding modes allows these two species to optimally exploit the variable and dynamic patchy distribution of planktonic resources.     

Generic delimitations of Central American Bignoniaceae

Generic delimitations in the Bignoniaceae are discussed, a number of Central American genera are reduced to synonymy, and a new genusPseudocatalpa is proposed. Generic mergers includeLevya withCydista, Saldanhaea withCuspidaria, Doxantha withMacfadyena, Pseudocalymma withPachyptera, andPhaedranthus withDistictis. New combinations necessitated by these mergers include the following:Arrabidaea costaricensis (Kränzl.) Gentry,A. pubescens (L.) Gentry,Cuspidaria floribunda (DC.) Gentry,C. weberbaueri (Spr.) Gentry,Cydista aequinoctialis var.hirtella (Benth.) Gentry,Distictis buccinatoria (DC.) Gentry,Macfadyena unguiscati (L.) Gentry,Melloa quadrivalvis (Jacq.) Gentry,Pachyptera alliacea (Lam.) Gentry,P. hymenaea (DC.) Gentry,P. kerere var.incarnata (Aubl.) Gentry,P. standleyi (Steyerm.) Gentry, andPseudocatalpa caudiculata (Standl.) Gentry. In addition, the fruits of several species are described for the first time, and their taxonomic significance is discussed.     

Temporal segregation in North American desert Membracidae

Summary Three species of Membracidae (Homoptera) have been found to coexist on the creosote bush, Larrea tridentata in the Mojave Desert. The insects are monophagous, univoltine and appear to avoid direct competition by temporal segregation. Multareis cornutus overwinters as slow growing nymphs and the adult population peaks in March. Centrodontus atlas overwinters in the egg stage with rapidly growing nymphs appearing in March while the adult population peaks in June. Multareoides bifurcatus overwinters as adults with the adult population peak in July. Nymphs occur in May–June. The various species have evolved cryptic form and coloration which is associated with phenology of the host plant. It is postulated that this has contributed to the evolution of temporal segregation.Study supported by Contract DE-AM03-76-SF00012 between the U.S. Department of Energy and the University of California, USA     

Temporal and Spatial Order in the Central Plains

Abstract

The major archeological complexes of the Central Plains can be arranged according to the Willey and Phillips system, thus recognizing not only content but time and space diemnsions.     

Diet-morphology correlations in the radiation of South American geophagine cichlids (Perciformes: Cichlidae: Cichlinae)

Genera within the South American cichlid tribe Geophagini display specialized feeding and reproductive strategies, with some taxa specialized for both substrate-sifting and mouth brooding. Several lineages within the clade also possess an epibranchial lobe (EBL), a unique pharyngeal structure that has been proposed to have a function in feeding and/or mouth brooding. A recently published genus-level phylogeny of Neotropical cichlids was used as the evolutionary framework for investigating the evolution of morphological features presumably correlated with diet and mouth brooding in the tribe Geophagini. We tested for possible associations between the geophagine epibranchial lobe and benthic feeding and mouth brooding. We also addressed whether the EBL may be associated with unique patterns of diversification in certain geophagine clades. Tests of binary character correlations revealed the EBL was significantly associated with mouth brooding. We also tested for a relationship between diet and morphology. We analyzed stomach contents and morphometric variation among 21 species, with data for two additional species obtained from the literature. Principal Components Analysis revealed axes of morphological variation significantly correlated with piscivory and benthivory, and both morphology and diet were significantly associated with phylogeny. These results suggest that the EBL could be an adaptation for either feeding or mouth brooding. The EBL, however, was not associated with species richness or accelerated rates of phyletic diversification.     

Temporal Changes in Randomness of Bird Communities across Central Europe

Many studies have examined whether communities are structured by random or deterministic processes, and both are likely to play a role, but relatively few studies have attempted to quantify the degree of randomness in species composition. We quantified, for the first time, the degree of randomness in forest bird communities based on an analysis of spatial autocorrelation in three regions of Germany. The compositional dissimilarity between pairs of forest patches was regressed against the distance between them. We then calculated the y-intercept of the curve, i.e. the ‘nugget’, which represents the compositional dissimilarity at zero spatial distance. We therefore assume, following similar work on plant communities, that this represents the degree of randomness in species composition. We then analysed how the degree of randomness in community composition varied over time and with forest management intensity, which we expected to reduce the importance of random processes by increasing the strength of environmental drivers. We found that a high portion of the bird community composition could be explained by chance (overall mean of 0.63), implying that most of the variation in local bird community composition is driven by stochastic processes. Forest management intensity did not consistently affect the mean degree of randomness in community composition, perhaps because the bird communities were relatively insensitive to management intensity. We found a high temporal variation in the degree of randomness, which may indicate temporal variation in assembly processes and in the importance of key environmental drivers. We conclude that the degree of randomness in community composition should be considered in bird community studies, and the high values we find may indicate that bird community composition is relatively hard to predict at the regional scale.     

Ecological variation in South American geophagine cichlids arose during an early burst of adaptive morphological and functional evolution

Diversity and disparity are unequally distributed both phylogenetically and geographically. This uneven distribution may be owing to differences in diversification rates between clades resulting from processes such as adaptive radiation. We examined the rate and distribution of evolution in feeding biomechanics in the extremely diverse and continentally distributed South American geophagine cichlids. Evolutionary patterns in multivariate functional morphospace were examined using a phylomorphospace approach, disparity-through-time analyses and by comparing Brownian motion (BM) and adaptive peak evolutionary models using maximum likelihood. The most species-rich and functionally disparate clade (CAS) expanded more efficiently in morphospace and evolved more rapidly compared with both BM expectations and its sister clade (GGD). Members of the CAS clade also exhibited an early burst in functional evolution that corresponds to the development of modern ecological roles and may have been related to the colonization of a novel adaptive peak characterized by fast oral jaw mechanics. Furthermore, reduced ecological opportunity following this early burst may have restricted functional evolution in the GGD clade, which is less species-rich and more ecologically specialized. Patterns of evolution in ecologically important functional traits are consistent with a pattern of adaptive radiation within the most diverse clade of Geophagini.     

Pliocene diversification within the South American Forest falcons (Falconidae: Micrastur)

The Neotropics are one of the most species rich regions on Earth, with over 3150 species of birds. This unrivaled biodiversity has been attributed to higher proportions of mountain ranges, tropical rain forest or rain fall in the forest than in any other major biogeographic regions. Five primary hypotheses aim to explain processes of diversification within the Neotropics; (1) the Pleistocene refuge hypothesis, (2) the riverine barrier hypothesis, (3) the Miocene marine incursions hypothesis, (4) the ecological gradient hypothesis, and (5) the impact of the last Andean uplift serving as a barrier between eastern and western population Andean populations. We assessed these hypotheses to see which best explained the species richness of the forest-falcons (Micrastur), a poorly known lineage of birds that inhabit lowland and mid-elevation humid forest. Our analyses suggest all speciation events within the genus Micrastur probably occurred in the last 2.5-3.6 myrs, at or before the Pliocene/Pleistocene boundary, with the basal split within the genus being 7 myrs old. Hence our data allow us to formerly reject the classical Pleistocene refuge for Micrastur, Our divergence time estimates are younger that dates for the Miocene marine incursions, the riverine barrier and the Andean uplift hypotheses.     

Lateralization of lateral displays in convict cichlids

We examine lateralization of lateral displays in convict cichlids, Amatitlania nigrofasciata, and show a population level preference for showing the right side. This enables contesting pairs of fish to align in a head-to-tail posture, facilitating other activities. We found individuals spent a shorter mean time in each left compared with each right lateral display. This lateralization could lead to contesting pairs using a convention to align in a predictable head-to-tail arrangement to facilitate the assessment of fighting ability. It has major implications for the common use of mirror images to study fish aggression, because the 'opponent' would never cooperate and would consistently show the incorrect side when the real fish shows the correct side. With the mirror, the 'normal' head-to-tail orientation cannot be achieved.     

Morphology, molecules, and character congruence in the phylogeny of South American geophagine cichlids (Perciformes, Labroidei)

Phylogenetic relationships among the Neotropical cichlid subfamily Geophaginae were examined using 136 morphological characters and a molecular dataset consisting of six mitochondrial and nuclear genes. Topologies produced by morphological and combined data under parsimony were contrasted, congruence among different partitions was analysed, and potential effects of character incongruence and patterns of geophagine evolution on phylogenetic resolution are discussed. Interaction of morphological and molecular characters in combined analysis produced better resolved and supported topologies than when either was analysed separately. Combined analyses recovered a strongly supported Geophaginae that was closely related to Cichlasomatinae. Within Geophaginae, two sister clades included all geophagine genera. Acarichthyini (Acarichthys+Guianacara) was sister to the ‘B clade’, which contained the ‘Geophagus clade’ (‘Geophagus’steindachneri+Geophagus sensu stricto, and both sister to Gymnogeophagus) as sister to the ‘Mikrogeophagus clade’ (Mikrogeophagus+‘Geophagus’brasiliensis), and in turn, the Geophagus and Mikrogeophagus clades were sister to the crenicarine clade (Crenicara+Dicrossus) and Biotodoma. The second geophagine clade included the ‘Satanoperca clade’ (Satanoperca+Apistogramma and Taeniacara) as sister to the ‘Crenicichla clade’ (Crenicichla+Biotoecus). Several lineages were supported by unique morphological synapomorphies: the Geophaginae + Cichlasomatinae (5 synapomorphies), Geophaginae (1), Crenicichla clade (3), crenicarine clade (1), the sister relationship of Apistogramma and Taeniacara (4) and of Geophagus sensu stricto and‘Geophagus’steindachneri (1), and the cichlasomine tribe Heroini (1). Incorporation of Crenicichla in Geophaginae reconciles formerly contradictory hypotheses based on morphological and molecular data, and makes the subfamily the most diverse and ecologically versatile clade of cichlids outside the African great lakes. Results of this study support the hypothesis that morphological differentiation of geophagine lineages occurred rapidly as part of an adaptive radiation.