Comparative cytogenetics in three Melipona species (Hymenoptera: Apidae) with two divergent heterochromatic patterns

Abstract The genus Melipona is subdivided into four subgenera based on morphological characteristics, and two groups based on cytogenetic patterns. The cytogenetic information on this genus is still scarce, therefore, the goal of this study was to characterize Melipona paraensis, Melipona puncticollis, and Melipona seminigra pernigra using the following techniques: C-banding, DAPI/CMA3 fluorochromes, and FISH with an 18S rDNA probe. Melipona paraensis (2n=18) and M. seminigra pernigra (2n=22) were classified as high heterochromatin content species (Group II). Their euchromatin is restricted to the ends of the chromosomes and is CMA3+; the 18S rDNA probe marked chromosome pair number 4. Melipona puncticollis (2n=18) is a low heterochromatin content species (Group I) with chromosome pair number 1 marked with CMA3 and 18S rDNA. Low heterochromatin content is a putative ancestral karyotype in this genus and high content is not a monophyletic trait (Melikerria presents species with both patterns). Differences concerning the karyotypic characteristics can be observed among Melipona species, revealing cytogenetic rearrangements that occurred during the evolution of this genus. Studies in other species will allow us to better understand the processes that shaped the chromatin evolution in Melipona.摘要：无刺蜂属（Melipona）依据形态学特征可划分为4个亚属，同时可根据细胞遗传学模式分为两类群。目前该属的细胞遗传学研究资料仍较为匮乏，因此本研究旨在采用C带显带、DAPI/CMA3荧光染色以及18S rDNA探针荧光原位杂交（FISH）技术，对帕拉无刺蜂（Melipona paraensis）、刻胸无刺蜂（Melipona puncticollis）以及半黑无刺蜂暗色亚种（Melipona seminigra pernigra）开展细胞遗传学特征分析。 其中，帕拉无刺蜂（2n=18）与半黑无刺蜂暗色亚种（2n=22）被归为高异染色质含量类群（类群II）：其常染色质仅分布于染色体末端，且呈CMA3阳性；18S rDNA探针可标记第4号染色体对。刻胸无刺蜂（2n=18）属于低异染色质含量类群（类群I），其第1号染色体对同时被CMA3染色与18S rDNA探针标记。 研究表明，低异染色质含量为该属的推测祖先核型，而高异染色质含量并非单系性状（Melikerria亚属包含兼具两类核型特征的物种）。无刺蜂属内不同物种间存在核型特征差异，揭示了该属演化过程中发生的细胞遗传学重排事件。后续针对更多物种的研究将有助于进一步阐明塑造无刺蜂属染色质演化的分子机制。