MEIOTIC CHROMOSOME COMPLEMENTS AND NUCLEAR DNA CONTENTS OF FOUR SPECIES OF SHRIMPS OF THE GENUS PENAEUS

Abstract

Meiotic chromosome spreads were prepared from testicular lobes of 4 species of penaeid shrimps to determine numbers of chromosomes and meiotic phases. DNA content of nuclei isolated from shrimp hemocytes of these species was estimated by flow cytometry. Meiotic chromosome spreads indicated that the haploid chromosome number of Penaeus aztecus, P. duorarum, and P. vannamei was 44, while that of P. setiferus was 45. These counts are consistent with diploid chromosome numbers reported previously for each of these species. No trivalents or quadrivalents were found in meiotic prophase. These 4 species had approximately the same genome size (approximately 70% of the human genome) as measured by flow cytometry. It is suggested that Robertsonian chromosome rearrangement has accompanied the speciation process in the genus Penaeus without polyploidization.