Phylogenetic relationships and the timing of evolutionary events are essential for understanding evolution on longer time scales. Cheilostome bryozoans are a group of ubiquitous, species-rich, marine colonial organisms with an excellent fossil record but lack phylogenetic relationships inferred from molecular data. We present genome-skimmed data for 395 cheilostomes and combine these with 315 published sequences to infer relationships and the timing of key events among c. 500 cheilostome species. We find that named cheilostome genera and species are phylogenetically coherent, rendering fossil or contemporary specimens readily delimited using only skeletal morphology. Our phylogeny shows that parental care in the form of brooding evolved several times independently but was never lost in cheilostomes. Our fossil calibration, robust to varied assumptions, indicates that the cheilostome lineage and parental care therein could have Paleozoic origins, much older than the first known fossil record of cheilostomes in the Late Jurassic.
Larger molecular phylogenies based on ever more genes are becoming commonplace with the advent of cheaper and more streamlined sequencing and bioinformatics pipelines. However, many groups of inconspicuous but no less evolutionarily or ecologically important marine invertebrates are still neglected in the quest for understanding species- and higher-level phylogenetic relationships. Here, we alleviate this issue by presenting the molecular sequences of 165 cheilostome bryozoan species from New Zealand waters. New Zealand is our geographic region of choice as its cheilostome fauna is taxonomically, functionally and ecologically diverse, and better characterized than many other such faunas in the world. Using this most taxonomically broadly-sampled and statistically-supported cheilostome phylogeny comprising 214 species, when including previously published sequences, we tested several existing systematic hypotheses based solely on morphological observations. We find that lower taxonomic level hypotheses (species and genera) are robust while our inferred trees did not reflect current higher-level systematics (family and above), illustrating a general need for the rethinking of current hypotheses. To illustrate the utility of our new phylogeny, we reconstruct the evolutionary history of frontal shields (i.e., a calcified bodywall layer in ascus-bearing cheilostomes) and asked if its presence has any bearing on the diversification rates of cheilostomes.
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25Resolution of relationships at lower taxonomic levels is crucial for answering many 26 evolutionary questions, and as such, sufficiently varied species representation is vital. This 27 latter goal is not always achievable with relatively fresh samples. To alleviate the difficulties 28 in procuring rarer taxa, we have seen increasing utilization of historical specimens in building 29 molecular phylogenies using high throughput sequencing. This effort, however, has mainly 30 focused on large-bodied or well-studied groups, with small-bodied and under-studied taxa 31 under-prioritized. Here, we present a pipeline that utilizes both historical and contemporary 32 specimens, to increase the resolution of phylogenetic relationships among understudied and 33 small-bodied metazoans, namely, cheilostome bryozoans. In this study, we pioneer 34 sequencing of air-dried bryozoans, utilizing a recent library preparation method for low DNA 35 input. We use the de novo mitogenome assembly from the target specimen itself as reference 36 for iterative mapping, and the comparison thereof. In doing so, we present mitochondrial and 37 ribosomal RNA sequences of 43 cheilostomes representing 37 species, including 14 from 38 historical samples ranging from 50 to 149 years old. The inferred phylogenetic relationships 39 of these samples, analyzed together with publicly available sequence data, are shown in a 40 statistically well-supported 65 taxa and 17 genes cheilostome tree. Finally, the 41 methodological success is emphasized by circularizing a total of 27 mitogenomes, seven from 42 historical cheilostome samples. Our study highlights the potential of utilizing DNA from 43 micro-invertebrate specimens stored in natural history collections for resolving phylogenetic 44 relationships between species. 45 46
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