Abstract
The unusual life style of Strepsiptera has presented a long-standing puzzle in establishing its affinity to other insects. Although Strepsiptera share few structural similarities with other insect orders, all members of this order share a parasitic life style with members of two distinctive families in the Coleoptera—the order now considered the most closely related to Strepsiptera based on recent genomic evidence. Among the structural features of several strepsipteran families and other insect families that have been surveyed are the organization of testes and ultrastructure of sperm cells. For comparison with existing information on insect sperm structure, this manuscript presents a description of testes and sperm of a representative of the most primitive extant strepsipteran family Mengenillidae, Eoxenos laboulbenei. We compare sperm structure of E. laboulbenei from this family with that of the three other families of Strepsiptera in the other strepsipteran suborder Stylopidia that have been studied as well as with members of the beetle families Meloidae and Rhipiphoridae that share similar life histories with Strepsiptera. Meloids, Rhipiphorids and Strepsipterans all begin larval life as active and viviparous first instar larvae. This study examines global features of these insects’ sperm cells along with specific ultrastructural features of their organelles.
Highlights
Sperm of insects show a great diversity of external shapes and sizes; and their internal ultrastructure is correspondingly complex and variable
We compare the sperm structure of E. laboulbenei from this primitive family with that of the three other families of Strepsiptera in the suborder Stylopidia studied so far (Xenidae, Elenchidae and Halictophagidae) as well as with members of two families in the Coleoptera2the most closely related neuropteroid order based on recent genomic evidence [6,7]
All Strepsiptera species examined previously and E. laboulbenei examined here have one sperm tube per testis [12]; within this one tube or follicle, all germ cells were represented by mature spermatozoa and did not show the parallel alignment of cells
Summary
Sperm of insects show a great diversity of external shapes and sizes; and their internal ultrastructure is correspondingly complex and variable. A basic ground plan exists for the sperm structure of all insects, and specific variations on this basic plan have proved to be useful characters in the study of insect phylogeny. These architectural features of insect sperm offer subcellular characters that may help resolve certain phylogenetic relationships that have stubbornly defied analysis using somatic characters [1,2]. We compare the sperm structure of E. laboulbenei from this primitive family with that of the three other families of Strepsiptera in the suborder Stylopidia studied so far (Xenidae, Elenchidae and Halictophagidae) as well as with members of two families in the Coleoptera2the most closely related neuropteroid order based on recent genomic evidence [6,7]. FRPSDUHV JOREDO IHDWXUHV RI WKHVH LQVHFWV¶ VSHUP FHOOV DORQJ ZLWK specific ultrastructural features of their organelles: (1) the flagella/nucleus interface; (2) acrosome/nucleus interface and (3) flagellar architecture revealed in transverse sections
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