Biology subjects

Pie, M. R.

Publications and source records attributed to Pie, M. R..

27 records · Page 2Linked to original sources

bioRxiv2020

An experimental assessment of the distribution of environmental DNA along the water column

The study of environmental DNA (eDNA) is increasingly becoming a valuable tool to survey and monitor aquatic communities. However, there are important gaps in our understanding of the dynamics governing the distribution of eDNA under natural conditions. In this report we carry out controlled experiments to assess the extent and timing of eDNA distribution along the water column. A sample of known eDNA concentration was placed at the bottom of a 5-m high tube (20 cm in diameter and total volume of 160 L), and water samples were obtained at different depths over an 8 h-period. The presence of the target eDNA was assessed by qPCR analysis. This sampling protocol allowed for assessing the timescale for the diffusion of eDNA while minimizing the influence of turbulence. We demonstrate that, after a time-period of as little as 30 min, the eDNA had spread across the entire container. The implications of these results for eDNA sampling protocols in the field are discussed.

ecology↗

bioRxiv2020

Mandibular morphology, task specialization, and bite mechanics in Pheidole ants (Hymenoptera: Formicidae)

The remarkable ecological and evolutionary success of ants was associated with the evolution of reproductive division of labor, in which sterile workers perform most colony tasks whereas reproductives become specialized in reproduction. In some lineages, the worker force became further subdivided into morphologically distinct subcastes (e.g. minor vs. major workers), allowing for the differential performance of particular roles in the colony. However, the functional and ecological significance of morphological differences between subcastes is not well understood. Here, we applied Finite Element Analysis (FEA) to explore the functional differences between major and minor ant worker mandibles. Analyses were carried out on mandibles of two Pheidole species, a dimorphic ant genus. In particular, we test whether major mandibles evolved to minimize stress when compared to minors using combinations of tooth and masticatory margin bites under strike and pressure conditions. Majors performed better in pressure conditions yet, contrary to our expectations, minors performed better in strike bite scenarios. Moreover, we demonstrate that even small morphological differences in ant mandibles might lead to substantial differences in biomechanical responses to bite loading. These results also underscore the potential of FEA to uncover biomechanical consequences of morphological differences within and between ant worker castes.

ecology↗

bioRxiv2020

The evolution of latitudinal range limits in tropical reef fishes: heritability, limits, and inverse Rapoport's rule

AimVariation in the size and position of geographical ranges is a key variable that underlies most biogeographical patterns. However, relatively little is known in terms of general principles driving their evolution, particularly in the marine realm. In this study we explore several fundamental properties regarding the evolution of reef fish latitudinal ranges, namely the degree of similarity in range size between ancestor and descendant lineages (i.e. phylogenetic signal); the evolution of range limits; and the latitudinal distribution of range sizes, particularly with respect to Rapoports rule. LocationGlobal. TaxonReef-associated fishes. MethodsWe integrate data on the latitudinal distribution and evolutionary history of 5,071 reef fish species with phylogenetic comparative methods to assess the level of phylogenetic signal in latitudinal range size, low- and high-latitude limits, and range midpoints, and to estimate rates of evolution of those traits. Finally, we test whether latitudinal ranges become smaller near the equator, as predicted by Rapoports rule, using phylogenetic generalized least squares. ResultsThere were varying levels of phylogenetic signal in latitudinal range size, low- and high-latitude limits, and range midpoints. Despite these differences, latitudinal midpoints were consistently shown to have the highest phylogenetic signal among all measured geographic features. Interestingly, the position of high-latitude limits in general evolved at substantially faster rates than their low-latitude counterparts. Finally, we confirm for the first time the existence of an inverse Rapoports rule in reef-associated fishes using phylogenetic comparative methods. Indeed, mean latitudinal range size of tropical species is nearly twice the size of their temperate counterparts (2067{+/-}1431 km vs. 1168{+/-}725 km, respectively). Main conclusionsWe uncovered several congruent patterns in phylogenetic signal and rates of evolution of latitudinal ranges, despite vastly disparate biogeographical distributions and ecological differences between the studied fish lineages. Such broad congruence across different taxa and oceans, as well as with previous data from terrestrial environments, suggests that the observed patterns might represent general principles governing geographical range evolution.

evolutionary biology↗

bioRxiv2020

Morphological evolution in the ant reproductive caste

The evolution of eusociality led to severe changes in the general hymenopteran body plan. In particular, the evolution of reproductive division of labour caused the worker caste to be largely freed from the demands involved in reproduction. As a consequence, workers were able to evolve highly specialized morphologies for foraging and colony maintenance, whereas the reproductive caste became specialized for reproduction. Despite these important changes, little is known about general patterns of morphological evolution within the ant reproductive caste. Our goals were to characterize morphological variation in the ant reproductive caste and to test whether different sexes display variation in their evolutionary rates. We obtained measurements of 897 specimens from a total of 678 ant species. The shapes of the size distributions were similar between sexes, with queens being larger than males in all traits except for eye length. Contrary to the expectation based on Renschs rule, although queens were larger, the degree of dimorphism increased with body size. Finally, there is strong evidence for an accelerated tempo of morphological evolution in queens in relation to males. These results represent the first comprehensive treatment of morphological variation in the ant reproductive caste and provide important new insights into their evolution.

evolutionary biology↗

bioRxiv2020

Worker-behavior and behavior-behavior interaction networks in the trap-jaw ant Odontomachus chelifer (Latreille, 1802)

Division of labor is among the main factors to explain the evolutionary success of social systems, from the origins of multicellularity to complex animal societies. The remarkable ecological success of social insects seems to have been largely driven by ergonomic advantages stemming from the behavioral specialization of workers. However, little is known about how individuals and their corresponding behavioral repertoires are related to each other within a division of labor context, particularly by viewing such relationships as complex networks. Applications of network theory to the study of social insects are almost exclusively used to analyze behavioral interactions between individuals, rather than to the study of relations among individuals and behaviors. Here, we use an approach to the study of the organization of the behavioral repertoire of ant colonies that considers both individual-behavior interactions and behavior-behavior interactions, besides colony time budgets. Our study investigates the organization of division of labor in colonies of the trap-jaw ant Odontomachus chelifer (LO_SCPLOWATREILLEC_SCPLOW, 1802). All the behavioral acts (including inactivity) performed within three queenright colonies of different sizes (n = 7, 30, and 60 workers) were studied under controlled laboratory conditions. Each ant was individually marked and observed by scan sampling in 10 min intervals for 10 h each (n = 5,919 behavioral acts). We describe the network topologies in terms of centrality, specialization, modularity, and nestedness. This study shows that workers of O. chelifer are organized according to structured networks, composed of individuals exhibiting varying degrees of specialization. The observed centrality scores indicate that some behaviors could have a disproportionately larger impact on the network organization (especially self-grooming). The results underscore the potential of the use of complex networks (particularly measures of modularity and nestedness) in order to discover and study novel organizational patterns of social groups in animal behavior.

animal behavior and cognition↗

bioRxiv2020

No evidence for discovery-dominance tradeoffs in Pheidole (Hymenoptera: Formicidae) assemblages

Understanding the mechanisms that allow species coexistence across spatial scales is of great interest to ecologists. Many such proposed mechanisms involve tradeoffs between species in different life-history traits, with distinct tradeoffs being expected to be prevalent at varying temporal and spatial scales. The dominance-discovery tradeoff posits that species differ in their ability to find and use resources quickly, in contraposition to their ability to monopolize those resources, a mechanism analogous to the competition-colonization tradeoff. We investigated the occurrence of this structuring mechanism in Pheidole (Hymenoptera: Formicidae) assemblages in Atlantic Forest remnants. According to the dominance-discovery tradeoff, we should observe a consistent interspecific variation along the axis of discovery and dominance. We established 55 sampling units across two sites, with each unit consisting of a sardine bait monitored for three hours. There was no distinction among Pheidole species in their ability to find or dominate food sources, suggesting that the dominance-discovery tradeoff does not explain their coexistence. The low levels of aggression between Pheidole species could prevent the establishment of dominance hierarchies, whereas the species order of arrival at food sources could allow for resource partitioning through priority effects.

ecology↗

bioRxiv2020

Evolution in Sinocyclocheilus cavefish is marked by rate shifts, reversals and origin of novel traits

Epitomized by the well-studied Astyanax mexicanus, cavefishes provide important model organisms to understand adaptations in response to divergent natural selection. However, the spectacular Sinocyclocheilus diversification of China, the most diverse cavefish clade in the world harboring nearly 75 species, demonstrate evolutionary convergence for many traits, yet remain poorly understood in terms of their morphological evolution. Here, using a broad sample of 49 species representative of this diversification, we analyze patterns of Sinocylocheilus evolution in a phylogenetic context. We categorized species into morphs based on eye-related condition: Blind, Micro-eyed (small-eyed), and Normal-eyed and we also considered three habitat types (Troglodytic - cave-restricted; Troglophilic - cave-associated; Surface - outside of caves). Geometric morphometric analyses show Normal-eyed morphs with fusiform shapes being segregated from Blind/Micro-eyed (Eye-regressed) morphs with deeper bodies along the first principal component ("PC") axis. The second PC axis accounts for shape complexity related to the presence of horns. Ancestral character reconstructions of morphs suggest at least three independent origins of Blind morphs, each with different levels of modification in relation to the typical morphology of ancestral Normal-eyed morphs. Interestingly, only some Blind or Micro-eyed morphs bear horns and they are restricted to a single clade (Clade B) and arising from a Troglodytic ancestral species. Our geophylogeny shows an east-to-west diversification spanning the Pliocene and the Pleistocene, with Troglodytic species dominating karstic subterranean habitats of the plains whereas predominantly Surface species inhabit streams and pools in hills to the west (perhaps due to the scarcity of caves). Integration of morphology, phylogeny and geography suggests Sinocyclocheilus are pre-adapted for cave dwelling. Analyses of evolutionary rates suggest that lineages leading to Blind morphs were characterized by significant rate shifts, such as a slowdown in body size evolution and a 3.3 to 12.5 fold increase in the evolutionary rate of eye regression. Furthermore, body size and eye size have undergone reversals, but horns have not, a trait that seem to require substantial evolutionary time to form. These results, compared to the Astyanax model system, indicate Sinocyclocheilus fishes demonstrate extraordinary morphological diversity and variation, offering an invaluable model system to explore evolutionary novelty.

evolutionary biology↗

bioRxiv2017

Phylogenomics of montane frogs of the Brazilian Atlantic Forest supports a scenario of isolation in sky islands followed by relative climatic stability

Despite encompassing a relatively small geographical area, montane regions harbor disproportionately high levels of species diversity and endemism. Yet, relatively little is known about the evolutionary mechanisms ultimately leading to montane diversity. In this study, we use target capture of ultraconserved elements to investigate the phylogenetic relationships and diversification patterns of Melanophryniscus (Bufonidae) and Brachycephalus (Brachycephalidae), two frog genera that occur in sky islands of the southern Atlantic Forest of Brazil. Specifically, we test whether diversification of montane species in these genera can be explained by a single climatic shift leading to isolation in sky islands, followed by relative climatic stability that maintained populations in allopatry. In both genera, the topologies inferred using concatenation and coalescent-based methods were concordant and had strong nodal support, except for a few recent splits. These recent splits tended to be supported by more informative loci (those with higher average bootstrap support), suggesting that, while individual trees may be well resolved, the relationships they recover are being obscured by non-informative data. Divergence dating of a combined dataset using both genera is consistent with concordant timing of their diversification. These results support the scenario of diversification-by-isolation in sky islands, and suggest that allopatry due to climatic gradients in montane regions are an important mechanism for generating species diversity and endemism in these regions.

evolutionary biology↗

bioRxiv2017

Phylogenomic Species Delimitation In Microendemic Frogs Of The Brazilian Atlantic Forest

The advent of next-generation sequencing allows researchers to use large-scale datasets for species delimitation analyses, yet one can envision an inflection point where the added accuracy of including more loci does not offset the increased computational burden. One alternative to including all loci could be to prioritize the analysis of loci for which there is an expectation of high informativeness, such as those with higher numbers of parsimony-informative sites. Here, we explore the issue of species delimitation and locus selection with species from two anuran genera: Melanophryniscus (Bufonidae) and Brachycephalus (Brachycephalidae). Montane species in these genera have been isolated in sky islands across the southern Brazilian Atlantic Forest, which led to the formation of a number of microendemic species. To delimit species, we obtained genetic data using target enrichment of ultraconserved elements from 32 populations (13 for Melanophryniscus and 19 for Brachycephalus), and we were able to create datasets that included over 800 loci with no missing data. We ranked loci according to their corresponding number of parsimony-informative sites, and we performed species delimitation analyses using BPP in each genus based on the top 10, 20, 40, 80, 160, 320, and 640 loci. We also conducted several additional analyses using 10 randomly sampled datasets containing the same numbers of loci to discriminate the relative contribution of increasing the number of loci from prioritizing those with higher informativeness. We identified three types of node: nodes with either consistently high or low support regardless of the number of loci or their informativeness, and nodes that were initially poorly supported, but their support became stronger with more data. Adding more loci had a stronger impact on model support than prioritizing loci for their informativeness, but this effect was less apparent in datasets with more than 160 loci. When viewed across all sensitivity analyses, our results suggest that the current species richness in both genera might have been underestimated. In addition, our results provide useful guidelines to the use of different sampling strategies to carry out species delimitation with phylogenomic datasets.

evolutionary biology↗