Adaptive Radiation and Evolution Within the Myxozoa

Abstract

Myxozoans are endoparasites characterized by extensive morphological simplification and complex life cycles. Their definitive hosts are bryozoans-in the case of the more primitive and species-poor Malacosporea, or annelids-in the case of the more derived and speciose Myxosporea. This chapter reviews patterns of adaptive radiation within the Myxozoa and explores the drivers that may have promoted evolutionary change. Topics covered include: multiple transitions between worm-like and sac-like forms in the Malacosporea; undersampling that likely limits our appreciation of malacosporean diversity; and multiple shifts between marine and freshwater environments in the Myxosporea. We also examine morphological simplification that is observed in stages that produce spores and associated changes in the size of these sporogonic stages. This contrasts with the evolution of morphological complexity in spores. Features proposed to be involved in diversification include the acquisition of hardened spores and plasmodia, a high diversity of definitive hosts and invasion of novel hosts and host environments in the

Assessing myxozoan presence and diversity using environmental DNA

“…The lineagespecific myxosporean assay detected 107 myxosporean OTUs associated with a diversity of aquatic environments. Phylogenetic placement of these OTUs indicates that a wide taxonomic range of 335 myxosporeans was successfully amplified with the same primer set, with putative taxa detected in both the freshwater and marine myxosporean lineages (Fiala et al, 2015). New OTUs (i.e.…”

“…There are two major clades, the early diverging and 50 species-poor Malacosporea and the highly derived and speciose Myxosporea (Fiala et al 2015).…”

“…Further challenges to revealing myxozoan diversity are presented by the general lack of informative features and by morphological convergence, both being related to the extreme morphological simplification that characterises myxozoans (Fiala et al, 2015). Sequence data are therefore crucial for identification and are widely included in taxonomic studies to ensure species discrimination 75 .…”

Morphology, ultrastructure and phylogeny of Myxobolus curimatae n. sp. (Myxozoa: Myxosporea) a parasite of Prochilodus costatus (Teleostei: Prochilodontidae) from the São Francisco River, Brazil

“…For this study, sixteen adult specimens of P. costatus (with average size of 34 [32][33][34][35][36][37][38][39][40] cm) were collected from the São Francisco River, in the city of Pirapora, Minas Gerais state, Brazil (17°12′75″S, 44°50′95″ W) in December 2011. The methodology of the present study was approved by the ethics research committee of Federal University of São Paulo (CEP: 0128/12), and is in accordance with Brazilian law.…”

Tetracapsuloides bryosalmonae abundance in river water

“…bryosalmonae is an endoparasite of freshwater bryozoans and salmonids, causing PKD in both wild and farmed fish in Europe (Wahli et al 2007) and North America (Ferguson & Needham 1978). Tetracapsuloides, Buddenbrockia and several undescribed species form the Malacosporea (Fiala et al 2015), a small and early diverging clade of myxozoans (Canning et al 2000). T. bryosalmonae spores (referred to as malacospores : Feist et al 2015) released in the urine of fish measure some 16 µm in width and 14 µm in height (Kent & Hedrick 1986, Hedrick et al 2004, Bettge et al 2009) and are infective to freshwater bryozoans (Morris & Adams 2006, Grabner & El-Matbouli 2008.…”