Cryptini

Santos, Bernardo F. & Brady, Seán G., 2024, Leveraging museum specimens, genomics and legacy datasets to unravel the phylogeny and biogeography of cryptin wasps (Hymenoptera, Ichneumonidae, Cryptini), Zoologica Scripta 53 (3), pp. 338-357 : 350-351

4.3 | Systematics and diversity of Cryptini

When comparing the cryptin fauna of different biogeographic zones, the Neotropical region had the highest level of phylogenetic diversity, but this was due to the larger number of species from that region represented in the tree; raw phylogenetic diversity is strongly dependent on the overall species richness because a larger number of species results in more branch lengths to be added up to the total index. When standardized by effect size, however, the Neotropical region showed relatively little phylogenetic dispersion, likely related to most of its representatives being concentrated in the Lymeon group— which is comprised almost exclusively of Neotropical taxa, with a few Nearctic offshoots (Figure 6). While there is no direct estimation of the timing of Cryptini diversification, existing divergence dating analyses including cryptins as outgroup taxa suggest that the group may be approximately 45–57 million years old ( Santos et al., 2021; Spasojevic et al., 2021), thus originating at a time when the continents were close to their current configuration. The distribution of Neotropical taxa in the cryptin tree is consistent with the idea that the group would have originated elsewhere and dispersed into the Neotropics through a few colonization events, each resulting in relatively large radiations. This would suggest that the current large number of species in the region results from a higher rate of net diversification ( Mittelbach et al., 2007), contra explanations that invoke a ‘time-for-speciation’ effect ( Jetz & Fine, 2012; Stephens & Wiens, 2003).

Indeed, some degree of ‘phylogenetic conservatism’ can be observed in the fauna of almost all regions, with communities significantly more phylogenetically clustered than it would be expected by a null, random model. The Oriental region showed the largest phylogenetic dispersion relative to its sample size, the only region where this metric did not differ significantly from the null model (p =.133). Members of almost all major clades are found in the Oriental region, which could potentially be an indicator that cryptins have been present in the area since the origin of the group, though investigating such a hypothesis would depend on formal historical biogeography analyses and a more thorough taxon sampling.

Our analyses of phylogenetic diversity should be viewed as preliminary: we have not achieved complete sampling at the generic level and the specieslevel taxonomic sampling represents only about 14% of the described diversity of Cryptini , with no specific sampling design to include the same proportion of the species found in each biogeographic region. It is possible, however, that our taxon sampling is not far from approximately reflecting the real species richness in each region: while that is not necessarily the case for all Ichneumonidae ( Quicke, 2012) , the Cryptini are certainly more species-rich in the tropics. Among tropical regions, Townes (1970) had estimated that the Neotropical region contains more species of Ichneumonidae than the Oriental or Afrotropical regions. There is also evidence that the Afrotropics are somewhat depauperate when compared to tropical regions in the Americas or Asia ( Raven et al., 2020). The representation in our dataset, however, certainly underestimates the fauna from the Palearctic region at the species level.

In our study, species of Cryptini were grouped in almost exactly the same larger groups as recovered by Santos (2017), though the relationships among some of the groups changed (Figure 8). Likewise, the relationships within groups were also often different than those in Santos (2017) – the SPR distance between the two trees when both trees were pruned to include only the overlapping taxa (i.e. the 370 original terminals of Santos, 2017) was of 64 SPR moves (subtree prune and regraft; see Bordewich & Semple, 2005). Herein we discuss the composition of each clade, with particular reference to the relationships of newly added taxa.