Phylogenetic relationships of toads of the Rhinella granulosa group (Anura: Bufonidae): a molecular perspective with comments on hybridization and introgression

The Rhinella granulosa group consists of 13 species of toads distributed throughout open areas of South America and Panama. In this paper we perform a phylogenetic analysis considering all but one species of the group, employing five nuclear and four mitochondrial genes, for up to 7910 bp per specimen. Separate phylogenetic analyses under direct optimization (DO) of nuclear and mitochondrial sequences recovered the R. granulosa group as monophyletic and revealed topological incongruence that can be explained mainly by multiple events of hybridization and introgression, both mitochondrial and nuclear. The DO combined analysis, after the exclusion of putatively introgressed or heterozygous genomes, resulted in a phylogenetic hypothesis for the R. granulosa group in which most of the species are recovered as monophyletic, but with interspecific relationships poorly supported. The optimization of morphological (adult and larval), chromosomal, and behavioural characters resulted in 12 putative phenotypic synapomorphies for this species group and some other synapomorphies for internal clades. Our results indicate the need for additional population genetic studies on R. dorbignyi and R. fernandezae to corroborate the taxonomic status of both taxa. Finally, we discuss biological and genetic characteristics of Bufonidae, as possible explanations for the common occurrence of hybridization and introgression observed in some lineages of this family.

颗粒蟾类群（Rhinella granulosa group）包含13种蟾蜍，分布于南美洲及巴拿马的开阔生境中。本研究对该类群除1种外的所有物种开展系统发育分析，共使用5个核基因与4个线粒体基因，单份标本的序列总长可达7910个碱基对。分别对核基因与线粒体序列进行直接优化法（direct optimization, DO）下的系统发育分析，结果均恢复出该类群为单系群，同时揭示了拓扑结构不一致现象，该现象主要可通过多次线粒体与核基因层面的杂交及渐渗事件解释。在剔除疑似渐渗或杂合的基因组后，联合数据集的直接优化法分析得到了颗粒蟾类群的系统发育假说：多数物种被恢复为单系群，但物种种间关系的支持度较低。对形态学（成体与幼体）、染色体及行为学特征进行优化后，本研究为该类群鉴定出12个推定的表型共源性状，同时为内部支系鉴定出若干其他共源性状。研究结果表明，需针对R. dorbignyi与R. fernandezae开展更多种群遗传学研究，以验证这两个类群的分类地位。最后，我们讨论了蟾蜍科（Bufonidae）的生物学与遗传学特征，以此解释该科部分支系中频繁出现的杂交与渐渗现象。