From Shelf to Slope: Evolutionary Transition from Niche Conservatism to Lability in Western Atlantic Burrowing Shrimps

The latitudinal diversity gradient (LDG) is a fundamental pattern in ecology, yet its understanding in marine systems remains largely constrained by the ‘tyranny’ of the shallow shelf, often ignoring the bathymetric dimension of the continental margin. This study provides a three-dimensional macroecological assessment of burrowing shrimps (Axiidea and Gebiidea) along the Western Atlantic (46° N–47° S), integrating 128 species and extending the bathymetric range to 1100 m. The results reveal a robust bimodal and asymmetric LDG that transcends the coastal shelf, characterized by an extensive high-diversity plateau in the Greater Caribbean region (~10–24° N) with an absolute peak of 46 species at 17° N. The persistent ‘tropical drop’ (0–10° N) is linked to the eco-physiological barrier created by the massive Amazon and Orinoco River plumes. Most significantly, I document the ‘Bathyal Paradox’: a radical evolutionary transition where the strong niche conservatism observed in shallow waters vanishes in the deep slope, indicating that the environmental stability of the deep slope promotes niche lability and clade-specific diversification. Furthermore, a consistent inverse Rapoport pattern across the entire water column confirms that regional climatic stability, rather than latitude alone, dictates geographical range geometry. This study provides a new conceptual framework for marine biodiversity, demonstrating that the integration of deep-sea data is essential to capture the true architecture of life in the ocean.