A new ancient lineage of frog (Anura: Nyctibatrachidae: Astrobatrachinae subfam. nov.) endemic to the Western Ghats of Peninsular India

The Western Ghats (WG) is an escarpment on the west coast of Peninsular India, housing one of the richest assemblages of frogs in the world, with three endemic families. Here, we report the discovery of a new ancient lineage from a high-elevation massif in the Wayanad Plateau of the southern WG. Phylogenetic analysis reveals that the lineage belongs to Natatanura and clusters with Nyctibatrachidae, a family endemic to the WG/Sri Lanka biodiversity hotspot. Based on geographic distribution, unique morphological traits, deep genetic divergence, and phylogenetic position that distinguishes the lineage from the two nyctibatrachid subfamilies Nyctibatrachinae Blommers-Schlösser, 1993 and Lankanectinae Dubois & Ohler, 2001, we erect a new subfamily Astrobatrachinae subfam. nov. (endemic to the WG, Peninsular India), and describe a new genus Astrobatrachus gen. nov. and species, Astrobatrachus kurichiyana sp. nov. The discovery of this species adds to the list of deeply divergent and monotypic or depauperate lineages with narrow geographic ranges in the southern massifs of the WG. The southern regions of the WG have long been considered geographic and climatic refugia, and this new relict lineage underscores their evolutionary significance. The small range of this species exclusively outside protected areas highlights the significance of reserve forest tracts in the WG in housing evolutionary novelty. This reinforces the need for intensive sampling to uncover new lineages and advance our understanding of the historical biogeography of this ancient landmass.

西高止山脉（Western Ghats, WG）是印度半岛西海岸的侵蚀断崖，拥有全球物种多样性最为丰富的蛙类类群之一，包含3个特有科。本文报道了采自南西高止山脉瓦亚纳德高原高海拔地块的一支全新古老演化支系。系统发育分析结果表明，该演化支系隶属于纳塔蟾类（Natatanura），并与仅分布于西高止山脉/斯里兰卡生物多样性热点地区的夜蛙科（Nyctibatrachidae）形成单系群。基于该演化支系的地理分布格局、独特的形态特征、显著的遗传分化，以及与夜蛙科两个亚科——1993年Blommers-Schlösser建立的夜蛙亚科（Nyctibatrachinae Blommers-Schlösser, 1993）和2001年Dubois与Ohler建立的兰卡蛙亚科（Lankanectinae Dubois & Ohler, 2001）——的系统发育位置差异，我们建立一新亚科：Astrobatrachinae subfam. nov.（仅分布于印度半岛西高止山脉），并描述一新属Astrobatrachus gen. nov.及新种Astrobatrachus kurichiyana sp. nov.。该新种的发现，进一步扩充了西高止山脉南部地块中，那些地理分布狭窄、高度分化且为单型或贫属的演化支系名录。长期以来，西高止山脉南部地区被视作地理与气候避难所，而这支全新的孑遗演化支系进一步凸显了其进化生物学意义。该物种的分布范围极小，且完全位于官方保护区之外，这一现状凸显了西高止山脉内的保护林区域在孕育进化新类群方面的核心价值。这一发现也强化了开展密集野外采样的必要性，以发掘更多新的演化支系，并深化我们对这一古老陆块历史生物地理学的认知。