Abstract
ABSTRACT Body size is a key factor in predicting the outcome of organisms’ interaction with their environment. A negative temperature–size relationship (TSR) is claimed to be one of the universal responses to climatic warming. Studies on extant biota also predicted that groups with narrow latitudinal range, tropical affinity, and higher body size would show higher sensitivity to climatic fluctuation. To confirm the generality of these relationships among marine ectotherms, we compiled the data on body size and global temperature over the Cenozoic using a global database of marine molluscs of Class Gastropoda and Bivalvia. Molluscan species do not show any signature of TSR for any taxonomic, regional, or ecological category during the Cenozoic. We did not find any evidence supporting heightened response in groups with limited latitudinal spread or with large body size. The body-size response of tropical species is not different from those of temperate species. Response of infauna and epifauna does not show any difference either and hence, refutes the predicted variation due to difference in their thermal-specialisation. Our results highlight the limited validity of ‘universal rules’ in explaining the climate-induced morphological response of marine communities in deep time and underscore the complexity in generalising the biotic outcome of climatic fluctuation.
Highlights
Body size of an organism has long been considered as one of the most important biological parameters because it is related to various physiological, life- history and ecological traits influencing community structure and functioning of ecosystem [1,2,3,4,5,6,7].Variations in body size, studied for many terrestrial ectotherms and endotherms, remains poorly understood for marine ectotherms especially in the context of temperature influence [8,9,10,11]
The overall effect of global warming on ecosystem is appreciated, but general rules to predict the fate of a specific group, as it responds to climate warming, is largely absent
The congruence between body size and temperature is observable only for raw data (ρ= -0.01; P= 0.02) (Fig 1) when body size and temperature estimates are both binned by geological stages; this relationship is not found in the detrended data, corrected for autocorrelation by first differencing (ρ= 0.18; P= 0.48) (Fig 2A), implying a lack of sizereduction due to climatic warming during Cenozoic
Summary
Body size of an organism has long been considered as one of the most important biological parameters because it is related to various physiological, life- history and ecological traits influencing community structure and functioning of ecosystem [1,2,3,4,5,6,7].Variations in body size, studied for many terrestrial ectotherms and endotherms, remains poorly understood for marine ectotherms especially in the context of temperature influence [8,9,10,11]. It has been recognized that many of the biological predictions about body size response to climatic variation, that have been developed primarily based on data from terrestrial vertebrates, are nonexistent or lack significance when applied for marine organisms [10]. Limitation of such extrapolation regained considerable interest in the present decades, primarily because of its relevance in the biotic response to recent climate crisis of global warming. This is especially true for marine ectotherms, though they represent more than 80% of the marine species on Earth [14, 15]
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