Browsing by Person "Ulmer, Jonah Michael"

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From glands to ground plans: Evolutionary morphology in Hymenoptera through space and time
(2023) Ulmer, Jonah Michael; Krogmann, Lars
Hymenoptera is one of the most species-rich and diverse groups of life, with over 153000 extant species described and another 2000 extinct. The evolutionary history of the group spans from the Triassic, around 250 million years ago, to the present day. In that time the order has spread and adapted to nearly every corner of the earth and nearly every conceivable ecological niche. That adaptation and time has led to innumerable forms and morphologies which have come and gone. Understanding the underlying patterns and impacts of these forms is perhaps the most fundamental and significant endeavor within systematics. In the first chapter, the earliest lineage of the megadiverse Chalcidoidea, Protoididae, is described from fourteen pieces of amber from the Lower Cretaceous, approximately 130 million years ago. Two genera and ten new species are described along with a key to the new family. This newly discovered stem-group chalcid provides unique insights into the early ground-plan of the superfamily which is investigated relative to other fossil and early crown-group lineages. From a thorough morphological investigation of the group, we evaluate the earliest forms of known plesiomorphies and hypothesize the transitionary forms of stem-group to crown-group chalcids. Due to its age, Protoitidae also allows us to examine the early transition of chalcids and their ground-plan relative to other early Proctotrupomorpha. Based on this study we provide palaeontological and morphological evidence for a late Cretaceous radiation in the superfamily and a modified hypothesis for the biogeographic origins of chalcid wasps. Based on the diversity of paleotaxa from the Cretaceous, an early, unsuccessful diversification event in the Cretaceous is hypothesized prior to the mega-radiation of the early Eocene. The presence of a “gap” in the paleocene record is also discussed and the utility of morphological data from the fossil record clarifies uncertainty in the parallelism versus secondary reversal in some characters in early crown-group lineages. Several ground-plan characters are confirmed from within the family, such as tarsal and antennomere counts, along with a putative plesiomorphy within Proctotrupomorpha of a strongly, proximally curving basal vein. In the second chapter, a metapleural gland is described from the parasitoid wasp Pelecinus polyturator. The unique gland is previously known only from Formicidae where it is hypothesized to be a key innovation in eusociality and an autapomorphy for the family. The gland is investigated both morphologically, behaviorally and chemically relative to the metapleural gland of ants. Hypotheses as to why the evolution of the gland was so impactful for ant diversification and less so for Pelecinidae are presented. The gland is shown to be the product of deep convergence within Hymenoptera due to a lack of transitional forms between the distantly related groups. Using this research as a basis, the “homology problem” of exocrine glands in insects is explored and formalized due to the presence of disparate evolutionary pathways occurring in a single organ system, the biosynthetic and morphological. Exaptation rather than adaptation is hypothesized to be the primary driver of glandular diversity in Hymenoptera. Within Pelecinidae, the gland ultrastructure and gross morphology is similar to that of the primitive ant lineages, suggesting a base form of the gland within Hymenoptera is present. The subsequent diversification and exaptation of the metapleural gland in Formicidae is hypothesized to be driven by eusociality, which is lacking in the asocial, parthenogenic pelecinids. A novel evolutionary model for examining exocrine glands is proposed with respect to underlying gene regulatory networks which signal the formation of exocrine glands in “hotspot” regions of the body while the biosynthetic pathways are highly homoplastic. Collectively, this work aims to elucidate the potential causes and effects of morphological “innovation” which leads to diversification in taxa. The examination of the earliest taxa of a hyper-diverse lineage provides insight into the ancestral states and morphology prior to radiation, and provides additional evidence for ground-plan characters. In lineages which have a dense radiation event such as Chalcidoidea, the transitionary forms of characters can be easily lost or obscured within a sparse fossil record, or overwhelmed by convergence and reversals across multiple lineages through time. Homoplasy can also be a boon for examining the impact of morphological innovation on diversification in a lineage relative to a convergent structure in a different group which is less successful.