Sequence heterochrony led to a gain of functionality in an immature stage of the central complex: A fly–beetle insight

Animal behavior is guided by the brain. Therefore, adaptations of brain structure and function are essential for animal survival, and each species differs in such adaptations. The brain of one individual may even differ between life stages, for instance, as adaptation to the divergent needs of larval and adult life of holometabolous insects. All such differences emerge during development, but the cellular mechanisms behind the diversification of brains between taxa and life stages remain enigmatic. In this study, we investigated holometabolous insects in which larvae differ dramatically from the adult in both behavior and morphology. As a consequence, the central complex, mainly responsible for spatial orientation, is conserved between species at the adult stage but differs between larvae and adults of one species as well as between larvae of different taxa. We used genome editing and established transgenic lines to visualize cells expressing the conserved transcription factor retinal homeobox, thereby marking homologous genetic neural lineages in both the fly Drosophila melanogaster and the beetle Tribolium castaneum. This approach allowed us for the first time to compare the development of homologous neural cells between taxa from embryo to the adult. We found complex heterochronic changes including shifts of developmental events between embryonic and pupal stages. Further, we provide, to our knowledge, the first example of sequence heterochrony in brain development, where certain developmental steps changed their position within the ontogenetic progression. We show that through this sequence heterochrony, an immature developmental stage of the central complex gains functionality in Tribolium larvae.

Sequence heterochrony led to a gain of functionality in an immature stage of the central complex: a fly-beetle insight

Animal behavior is guided by the brain. Therefore, adaptations of brain structure and function are essential for animal survival, and each species differs in such adaptations. The brain of one individual may even differ between life stages, for instance as adaptation to the divergent needs of larval and adult life of holometabolous insects. All such differences emerge during development but the cellular mechanisms behind the diversification of brains between taxa and life stages remain enigmatic. In this study, we investigated holometabolous insects, where larvae differ dramatically from the adult in both behavior and morphology. As consequence, the central complex, mainly responsible for spatial orientation, is conserved between species at the adult stage, but differs between larvae and adults as well as between larvae of different taxa. We used genome editing and established transgenic lines to visualize cells expressing the conserved transcription factor retinal homeobox, thereby marking homologous genetic neural lineages in both the fly Drosophila melanogaster and the beetle Tribolium castaneum. This approach allowed us for the first time to compare the development of homologous neural cells between taxa from embryo to the adult. We found complex heterochronic changes including shifts of developmental events between embryonic and pupal stages. Further, we provide, to our knowledge, the first example of sequence heterochrony in brain development, where certain developmental steps changed their position within the ontogenetic progression. We show that through this sequence heterochrony, an immature developmental stage of the central complex gains functionality in Tribolium larvae. We discuss the bearing of our results on the evolution of holometabolous larval central complexes by regression to a form present in an ancestor.

‘Tampering with the Expected Sequence’: Heterochrony and Sex Change in Orlando

This chapter reads the fantastical sex-change and longevity in Woolf’s Orlando in relation to contemporary experiments on the genetic and developmental determination of sex, notably the concept of heterochrony. The chapter argues that Orlando’s transformation from man to woman should be read literally, as a metamorphic change in the protagonist’s body; the embodied nature and the specific manifestations of the metamorphosis are designed to counter the recapitulatory plot that inheres in sexological discourses of the day. The corporeality of the Orlando’s development is rarely acknowledged in queer and feminist studies, which tend to emphasise gender and performance at the expense of sex and embodiment. By linking Woolf’s novel to contemporary biology, I complicate this common view and provide a positive alternative to the correlative argument that Orlando’s sex change amounts to a mere wish-fulfillment fantasy.

Skeletal development in the African elephant and ossification timing in placental mammals

We provide here unique data on elephant skeletal ontogeny. We focus on the sequence of cranial and post-cranial ossification events during growth in the African elephant ( Loxodonta africana ). Previous analyses on ossification sequences in mammals have focused on monotremes, marsupials, boreoeutherian and xenarthran placentals. Here, we add data on ossification sequences in an afrotherian. We use two different methods to quantify sequence heterochrony: the sequence method and event-paring/Parsimov. Compared with other placentals, elephants show late ossifications of the basicranium, manual and pedal phalanges, and early ossifications of the ischium and metacarpals. Moreover, ossification in elephants starts very early and progresses rapidly. Specifically, the elephant exhibits the same percentage of bones showing an ossification centre at the end of the first third of its gestation period as the mouse and hamster have close to birth. Elephants show a number of features of their ossification patterns that differ from those of other placental mammals. The pattern of the initiation of the ossification evident in the African elephant underscores a possible correlation between the timing of ossification onset and gestation time throughout mammals.