Most fishes live in shallow waters, which tend to be warm, productive and complex. Yet, ~20% of ray-finned fish species have successfully colonized the deep sea (below 200 meters). In a study published in PNAS, we aimed to explain why fewer species live in the deep sea versus shallow waters. We found two surprising results:
(1) Over the past 200 million years, speciation rate peaks alternated between shallow-water and deep sea fishes. When Earth's climate was warm, shallow fishes tended to be favored; when climate was cooler, deep-sea fishes tended to be favored (that is, the lower species richness of deep-sea fishes today cannot be explained simply by lower speciation rates).
(2) A possible explanation could be that not all fishes are capable of colonizing the deep sea. We used morphological data measured from museum specimens to show that lineages that successfully colonized the deep sea looked differently from the start: they tended to have larger jaws, or more tapered tails, than the average fish. This is an example of exaptation: features that evolved in one context turn out to be beneficial in a new context later on. It also means that not all fishes can "hack it" in the deep sea.
(1) Over the past 200 million years, speciation rate peaks alternated between shallow-water and deep sea fishes. When Earth's climate was warm, shallow fishes tended to be favored; when climate was cooler, deep-sea fishes tended to be favored (that is, the lower species richness of deep-sea fishes today cannot be explained simply by lower speciation rates).
(2) A possible explanation could be that not all fishes are capable of colonizing the deep sea. We used morphological data measured from museum specimens to show that lineages that successfully colonized the deep sea looked differently from the start: they tended to have larger jaws, or more tapered tails, than the average fish. This is an example of exaptation: features that evolved in one context turn out to be beneficial in a new context later on. It also means that not all fishes can "hack it" in the deep sea.
Some anglerfishes have tiny teeth! The deep sea is a food-limited environment; species in the bathypelagic zone depend on food raining down from surface waters. We think deep-sea fishes should be opportunistic feeders since they never know when their next meal will come along. We analyzed CT scans (3D x-ray images) of anglerfish jaws and found surprising diversity in their teeth. Shouldn't all anglerfishes evolve the biggest possible teeth to catch any prey that comes along? This is an unsolved mystery that shows how much we have left to learn about deep-sea fishes!
Key publications and grants:
NSF Postdoctoral Fellowship: Tempo and mode in the abyss: evolution following colonization of the deep sea
Miller, E. C., C. M. Martinez, S. T. Friedman, P. C. Wainwright, S. A. Price, and L. Tornabene. 2022. Alternating regimes of shallow and deep-sea diversification explain a species richness paradox in marine fishes. Proceedings of the National Academy of Sciences, 199, e2123544119.
Heiple, Z., J. M. Huie, A. Medeiros, P. Hart, C. Goatley, D. Arcila, and E.C. Miller. 2023. Many ways to build an angler: An analysis of feeding morphologies in a deep-sea evolutionary radiation. Biology Letters, 19: 20230049.
UW News: Study reveals how ancient fish colonized the deep sea
NSF Postdoctoral Fellowship: Tempo and mode in the abyss: evolution following colonization of the deep sea
Miller, E. C., C. M. Martinez, S. T. Friedman, P. C. Wainwright, S. A. Price, and L. Tornabene. 2022. Alternating regimes of shallow and deep-sea diversification explain a species richness paradox in marine fishes. Proceedings of the National Academy of Sciences, 199, e2123544119.
Heiple, Z., J. M. Huie, A. Medeiros, P. Hart, C. Goatley, D. Arcila, and E.C. Miller. 2023. Many ways to build an angler: An analysis of feeding morphologies in a deep-sea evolutionary radiation. Biology Letters, 19: 20230049.
UW News: Study reveals how ancient fish colonized the deep sea