Papers on sexual selection often highlight the incredible diversity of sexually selected traits across animals. Yet, few studies have tried to explain why this diversity evolved. Animals use many different types of traits to attract mates and outcompete rivals, including colours, songs, and horns, but it remains unclear why, for example, some taxa have songs, others have colours, and others horns. Here, we first conduct a systematic survey of the basic diversity and distribution of different types of sexually selected signals and weapons across the animal Tree of Life. Based on this survey, we describe seven major patterns in trait diversity and distributions. We then discuss 10 unanswered questions raised by these patterns, and how they might be addressed. One major pattern is that most types of sexually selected signals and weapons are apparently absent from most animal phyla (88%), in contrast to the conventional wisdom that a diversity of sexually selected traits is present across animals. Furthermore, most trait diversity is clustered in Arthropoda and Chordata, but only within certain clades. Within these clades, many different types of traits have evolved, and many types appear to have evolved repeatedly. By contrast, other major arthropod and chordate clades appear to lack all or most trait types, and similar patterns are repeated at smaller phylogenetic scales (e.g. within insects). Although most research on sexual selection focuses on female choice, we find similar numbers of traits (among sampled species) are involved in male contests (44%) and female choice (55%). Overall, these patterns are largely unexplained and unexplored, as are many other fundamental questions about the evolution of these traits. We suggest that understanding the diversity of sexually selected traits may require a shift towards macroevolutionary studies at relatively deep timescales (e.g. tens to hundreds of millions of years ago).

Tissue sample databases housed in biodiversity archives represent a vast trove of genetic resources, and these tissues are often destructively subsampled and provided to researchers for DNA extractions and subsequent sequencing. While obtaining a sufficient quantity of DNA for downstream applications is vital for these researchers, it is also important to preserve tissue resources for future use given that the original material is destructively and consumptively sampled with each use. It is therefore necessary to develop standardized tissue subsampling and loaning procedures to ensure that tissues are being used efficiently. In this study, we specifically focus on the efficiency of DNA extraction methods by using anuran liver and muscle tissues maintained at a biodiversity archive. We conducted a series of experiments to test whether current practices involving coarse visual assessments of tissue size are effective, how tissue mass correlates with DNA yield and concentration, and whether the amount of DNA recovered is correlated with sample age. We found that tissue samples between 2 and 8 mg resulted in the most efficient extractions, with tissues at the lower end of this range providing more DNA per unit mass and tissues at the higher end of this range providing more total DNA. Additionally, we found no correlation between tissue age and DNA yield. Because we find that even very small tissue subsamples tend to yield far more DNA than is required by researchers for modern sequencing applications (including whole genome shotgun sequencing), we recommend that biodiversity archives consider dramatically improving sustainable use of their archived material by providing researchers with set quantities of extracted DNA rather than with the subsampled tissues themselves.

Tissue sample databases housed in biodiversity archives represent a vast trove of genetic resources, and these tissues are frequently destructively subsampled and provided to researchers for DNA extractions and subsequent sequencing. While obtaining a sufficient quantity of DNA for downstream applications is vital for these researchers, it is also important to preserve tissue resources for future use given that the original material is destructively and consumptively sampled with each use. It is therefore necessary to develop standardized tissue subsampling and loaning procedures to ensure that tissues are being used efficiently. In this study, we specifically focus on the efficiency of DNA extraction methods by using anuran liver and muscle tissues maintained at a biodiversity archive. We conducted a series of experiments to test whether current practices involving coarse visual assessments of tissue size are effective, how tissue mass correlates with DNA yield and concentration, and whether the amount of DNA recovered is correlated with sample age. We found that tissue samples between 2 mg and 8 mg resulted in the most efficient extractions, with tissues at the lower end of this range providing more DNA per unit mass and tissues at the higher end of this range providing more total DNA.Additionally, we found no correlation between tissue age and DNA yield. Because we find that even very small tissue subsamples tend to yield far more DNA than is required by researchers for modern sequencing applications (including whole genome shotgun sequencing), we recommend that biodiversity archives consider dramatically improving sustainable use of their archived material by providing researchers with set quantities of extracted DNA rather than with the subsampled tissues themselves.PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.

Tissue sample databases housed in biodiversity archives represent a vast trove of genetic resources, and these tissues are frequently destructively subsampled and provided to researchers for DNA extractions and subsequent sequencing. While obtaining a sufficient quantity of DNA for downstream applications is vital for these researchers, it is also important to preserve tissue resources for future use given that the original material is destructively and consumptively sampled with each use. It is therefore necessary to develop standardized tissue subsampling and loaning procedures to ensure that tissues are being used efficiently. In this study, we specifically focus on the efficiency of DNA extraction methods by using anuran liver and muscle tissues maintained at a biodiversity archive. We conducted a series of experiments to test whether current practices involving coarse visual assessments of tissue size are effective, how tissue mass correlates with DNA yield and concentration, and whether the amount of DNA recovered is correlated with sample age. We found that tissue samples between 2 mg and 8 mg resulted in the most efficient extractions, with tissues at the lower end of this range providing more DNA per unit mass and tissues at the higher end of this range providing more total DNA.Additionally, we found no correlation between tissue age and DNA yield. Because we find that even very small tissue subsamples tend to yield far more DNA than is required by researchers for modern sequencing applications (including whole genome shotgun sequencing), we recommend that biodiversity archives consider dramatically improving sustainable use of their archived material by providing researchers with set quantities of extracted DNA rather than with the subsampled tissues themselves.PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.