Showing papers by "Nicholas J. Strausfeld published in 2019"

Mushroom bodies in crustaceans: Insect-like organization in the caridid shrimp Lebbeus groenlandicus

Abstract: Paired centers in the forebrain of insects, called the mushroom bodies, have become the most investigated brain region of any invertebrate due to novel genetic strategies that relate unique morphological attributes of these centers to their functional roles in learning and memory. Mushroom bodies possessing all the morphological attributes of those in dicondylic insects have been identified in mantis shrimps, basal hoplocarid crustaceans that are sister to Eumalacostraca, the most species-rich group of Crustacea. However, unless other examples of mushroom bodies can be identified in Eumalacostraca, the possibility is that mushroom body-like centers may have undergone convergent evolution in Hoplocarida and are unique to this crustacean lineage. Here, we provide evidence that speaks against convergent evolution, describing in detail the paired mushroom bodies in the lateral protocerebrum of a decapod crustacean, Lebbeus groenlandicus, a species belonging to the infraorder Caridea, an ancient lineage of Eumalacostraca.

The Divergent Evolution of Arthropod Brains

Abstract: Occasionally, fossils recovered from lower and middle Cambrian sedimentary rocks contain the remains of nervous system. These residues reveal the symmetric arrangements of brain and ganglia that correspond to the ground patterns of brain and ventral ganglia of four major panarthropod clades existing today: Onychophora, Chelicerata, Myriapoda, and Pancrustacea. Comparative neuroanatomy of living species and studies of fossils suggest that highly conserved neuronal arrangements have been retained in these four lineages for more than a half billion years, despite some major transitions of neuronal architectures. This chapter will review recent explorations into the evolutionary history of the arthropod brain, concentrating on the subphylum Pancrustacea, which comprises hexapods and crustaceans, and on the subphylum Chelicerata, which includes horseshoe crabs, scorpions, and spiders. Studies of Pancrustacea illustrate some of the challenges in ascribing homology to centers that appear to have corresponding organization, whereas Chelicerata offers clear examples of both divergent cerebral evolution and convergence.

Ancestral Regulatory Mechanisms Specify Conserved Midbrain Circuitry in Arthropods and Vertebrates

Abstract: Corresponding attributes of neural development and function suggest arthropod and vertebrate brains may have an evolutionarily conserved organization. However, the underlying mechanisms have remained elusive. Here we identify a gene regulatory and character identity network defining the deutocerebral-tritocerebral boundary (DTB) in Drosophila. We show this network comprises genes homologous to those directing midbrain-hindbrain boundary (MHB) formation in vertebrates and their closest chordate relatives. Genetic tracing reveals that the embryonic DTB gives rise to adult midbrain circuits that in flies control auditory and vestibular information processing and motor coordination, as do MHB-derived circuits in vertebrates. DTB-specific gene expression and function is directed by cis-regulatory elements (CREs) of developmental control genes that include homologs of mammalian Zinc finger of the cerebellum and Purkinje cell protein 4. Moreover, Drosophila DTB-specific CREs correspond to regulatory sequences of human ENGRAILED-2, PAX-2 and DACHSHUND-1 that direct MHB-specific expression in the embryonic mouse brain. Together, these findings imply ancestral regulatory mechanisms mediating the genetic specification of midbrain-cerebellar circuitry for balance and motor control that may predated the radiation of cephalic nervous systems across the animal kingdom.

Mushroom body homology and divergence across pancrustacea

Abstract: Descriptions of crustacean brains have mainly focused on three highly derived lineages: the reptantian infraorders represented by spiny lobsters, lobsters, and crayfish. Those descriptions advocate the view that dome- or cap-like neuropils, referred to as hemiellipsoid bodies, are the ground pattern organization of centers that are comparable to insect mushroom bodies in processing olfactory information. Here we challenge the doctrine that hemiellipsoid bodies are a derived trait of crustaceans, whereas mushroom bodies are a derived trait of hexapods. We demonstrate that mushroom bodies typify lineages that arose before Reptantia and exist in Reptantia. We show that evolved variations of the mushroom body ground pattern are, in some lineages, defined by extreme diminution or loss and, in others, by the incorporation of mushroom body circuits into lobeless centers. Such transformations are ascribed to modifications of the columnar organization of mushroom body lobes that, as shown in Drosophila and other hexapods, contain networks essential for learning and memory. We propose that lobed mushroom bodies distinguish crustaceans that negotiate the multidimensionality of complex ecologies, where continuous updating of multistimulus valence and memory is paramount.