Reproductive histology of Tomeurus gracilis Eigenmann, 1909 (Teleostei: Atherinomorpha: Poeciliidae) and the evolution of viviparity in atherinomorph fishes

L. PARENTI; F. LO NOSTRO; H. GRIER

JOURNAL OF MORPHOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Año: 2010 vol. 271 p. 1399 - 1406

0362-2525

Tomeurus gracilis is a species long consid-ered pivotal in understanding the evolution of livebear-ing in atherinomorph fishes. Tomeurus gracilis is a zygo-parous or embryoparous poeciliid: internal fertilizationis followed by females laying fertilized eggs singly orretaining fertilized eggs until or near hatching. Tomeu-rus was hypothesized as the sister group of the vivipa-rous poeciliids until it was proposed as a close relativeof a derived viviparous poeciliid, Cnesterodon, hencenested among viviparous taxa rather than near the rootof the tree. Here, we describe and compare reproductivemorphological characters of the little-known Tomeuruswith those of representative atherinomorphs. In Tomeu-rus and Cnesterodon, sperms are packaged in nakedsperm bundles, or spermatozeugmata, in a configurationconsidered here diagnostic of viviparous poeciliids.Testes are single and free sperm are stored in the ovaryin both taxa in contrast to oviparous atherinomorphs inwhich testes are paired and sperm are not packaged andnot stored in the ovary. Efferent ducts in Cnesterodontestes and other viviparous poeciliids have a PAS-posi-tive secretion demonstrating presence of a glycoproteinthat inactivates sperm or prevents final sperm matura-tion. No PAS-positive staining secretion was observedin Tomeurus or oviparous atherinomorphs. Tomeurusshares apomorphic reproductive characters, such assperm bundle and testis morphology and a gonopodium,with viviparous poeciliids and plesiomorphic characters,such as a thick zona pellucida with filaments, with ovip-arous taxa. We do not postulate loss or reversal of vivi-parity in Tomeurus, and we corroborate its phylogeneticposition as sister to the viviparous poeciliids.