Diversification rates in Tardigrada indicate a decreasing tempo of lineage splitting regardless of reproductive mode

Abstract

Understanding the dynamics of speciation and extinction events is one of the most interesting subjects in evolutionary biology that relates to all life forms, even the smallest ones. Tardigrades are microscopic invertebrates that attracted public and scientific attention mostly due to their ability to enter into the diapause stage called cryptobiosis and in such stage resist extremely harsh environmental conditions. However, although recent research solved a considerable number of phylogenetic uncertainties and further uncovered physiological mechanisms of cryptobiosis, not much attention is given to the evolutionary forces shaping tardigrade diversity. Here, we investigated the effect of reproductive mode on diversification rates in tardigrades using three groups: macrobiotids, echiniscids and milnesids, which represent low, moderate and high levels of parthenogenesis, respectively. Our results showed a decreasing tempo of diversification events for each of the studied groups without any differences that could be ascribed to reproductive mode. We discussed the observed lack of effect in tardigrades acknowledging deficiencies in available data sets and encouraging further studies to understand whether our results can be considered reliable.

Integrative taxonomy reveals new, widely distributed tardigrade species of the genus Paramacrobiotus (Eutardigrada: Macrobiotidae)

“…Although the results indicate considerable diversity that is still hidden within the genus, it should be also noted that in our study more putative species were delimited by tree-based methods compared with distance-based methods. However, this finding is in line with recent studies on tardigrades, but also studies on other animal groups 85 – 87 . Based on the research which examined numerous Paramacrobiotus populations 14 , 15 , we can notice that many species in this genus (especially in the Pam.…”