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Evidence of parallel evolution in the dental elements of Sweetognathus conodonts.

ABSTRACT: The repeated emergence of similar morphologies in the dental elements of Permian Sweetognathus conodonts has been a hypothesized example of parallel evolution. To test if morphological parallelisms occur between isolated Sweetognathus lineages, this study uses two-dimensional-based geometric morphometrics combined with a revised and expanded phylogeny of Permian Sweetognathus conodonts to quantify dental element trait distributions and compare the phenotypic trajectories between lineages. A hierarchical clustering method was used to identify recurrent species pairs based on principal component scores describing their morphological variation, with the further incorporation of widely used ecological metrics such as limiting similarity and morphological overlap. Our research implies that a major contributor to conodont diversity in Palaeozoic marine trophic networks is the emergence of recurrent parallel morphologies via disruptive and directional selection. This study illustrates the mechanisms through which conodonts achieved their status as hyper-diverse predators and scavengers, contributing substantially to the complexity of Palaeozoic marine communities.

SUBMITTER: Petryshen W

PROVIDER: S-EPMC7739493 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature

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Evidence of parallel evolution in the dental elements of Sweetognathus conodonts.

Petryshen W W Henderson C M CM De Baets K K Jarochowska E E

Proceedings. Biological sciences 20201118 1939

The repeated emergence of similar morphologies in the dental elements of Permian Sweetognathus conodonts has been a hypothesized example of parallel evolution. To test if morphological parallelisms occur between isolated Sweetognathus lineages, this study uses two-dimensional-based geometric morphometrics combined with a revised and expanded phylogeny of Permian Sweetognathus conodonts to quantify dental element trait distributions and compare the phenotypic trajectories bet ...[more]

PMID: 33203328

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Project description:Antagonistic interactions between bacteriophage (phage) and its bacterial host drives the continual selection for resistance and counter-defence. To date, much remains unknown about the genomic evolution that occurs as part of the underlying mechanisms. Such is the case for the marine cyanobacteria Synechococcus and viruses (cyanophages) that infect them. Here, we monitored host and phage abundances, alongside genomic changes to the phage populations, in a 500-day (~55 bacterial generations) infection experiment between Synechococcus sp. WH7803 and the T4-type cyanophage S-PM2d, run parallel in three replicate chemostats (plus one control chemostat). Flow cytometric count of total abundances revealed relatively similar host-phage population dynamics across the chemostats, starting with a cycle of host population collapse and recovery that led to phases of host-phage coexistence. Whole-genome analysis of the S-PM2d populations detected an assemblage of strongly selected and repeatable genomic changes, and therefore parallel evolution in the phage populations, early in the experiment (sampled on day 39). These consisted mostly of non-synonymous single-nucleotide-polymorphisms and a few instances of indel, altogether affecting 18 open-reading-frames, the majority of which were predicted to encode virion structures including those involved in phage adsorption onto host (i.e., baseplate wedge, short tail fibre, adhesin component). Mutations that emerged later (sampled on day 500), on the other hand, were found at a larger range of frequencies, with many lacking repeatability across the chemostats. This is indicative of some degree of between-population divergence in the phage evolutionary trajectory over time. A few of the early and late mutations were detected within putative auxiliary metabolic genes, but these generally occurred in only one or two of the chemostats. Less repeatable mutations may have higher fitness costs, thus drawing our attention onto the role of trade-offs in modulating the trajectory of a host-phage coevolution.

Project description:Conodonts were the first vertebrates to develop mineralized dental tools, known as elements. Recent research suggests that conodonts were macrophagous predators and/or scavengers but we do not know how this feeding habit emerged in the earliest coniform conodonts, since most studies focus on the derived, 'complex' conodonts. Previous modelling of element position and mechanical properties indicate they were capable of food processing. A direct test would be provided through evidence of in vivo element crown tissue damage or through in vivo incorporated chemical proxies for a shift in their trophic position during ontogeny. Here we focus on coniform elements from two conodont taxa, the phylogenetically primitive Proconodontus muelleri Miller, 1969 from the late Cambrian and the more derived Panderodus equicostatus Rhodes, 1954 from the Silurian. Proposing that this extremely small sample is, however, representative for these taxa, we aim to describe in detail the growth of an element from each of these taxa in order to the test the following hypotheses: (1) Panderodus and Proconodontus processed hard food, which led to damage of their elements consistent with prey capture function; and (2) both genera shifted towards higher trophic levels during ontogeny. We employed backscatter electron (BSE) imaging, energy-dispersive X-ray spectroscopy (EDX) and synchrotron radiation X-ray tomographic microscopy (SRXTM) to identify growth increments, wear and damage surfaces, and the Sr/Ca ratio in bioapatite as a proxy for the trophic position. Using these data, we can identify whether they exhibit determinate or indeterminate growth and whether both species followed linear or allometric growth dynamics. Growth increments (27 in Pa. equicostatus and 58 in Pr. muelleri) were formed in bundles of 4-7 increments in Pa. equicostatus and 7-9 in Pr. muelleri. We interpret the bundles as analogous to Retzius periodicity in vertebrate teeth. Based on applied optimal resource allocation models, internal periodicity might explain indeterminate growth in both species. They also allow us to interpret the almost linear growth of both individuals as an indicator that there was no size-dependent increase in mortality in the ecosystems where they lived e.g., as would be the case in the presence of larger predators. Our findings show that periodic growth was present in early conodonts and preceded tissue repair in response to wear and damage. We found no microwear and the Sr/Ca ratio, and therefore the trophic position, did not change substantially during the lifetimes of either individual. Trophic ecology of coniform conodonts differed from the predatory and/or scavenger lifestyle documented for "complex" conodonts. We propose that conodonts adapted their life histories to top-down controlled ecosystems during the Nekton Revolution.

Dataset Information

Evidence of parallel evolution in the dental elements of Sweetognathus conodonts.

Publications

Evidence of parallel evolution in the dental elements of <i>Sweetognathus</i> conodonts.

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