Creationism in Crisis - Rapid Evolution of Codfish Caused by Human Predation

Creationism in Crisis

Rapid Evolution of Codfish Caused by Human Predation

Codfish drying in Lofoten, Norway, illustrating the region's classical long-term fishing tradition. Scientists collected historical and contemporary genetic samples at Lofoten for a study on evolutionary changes in codfish.

Giada Ferrari

Atlantic cod, Gadus morhua

Overfishing Linked to Rapid Evolution of Codfish | Rutgers University

Just as the theory of evolution predicts, codfish have evolved under the selection pressure of human predation, and this evolution has occurred over the second half of the 20th century when the policy had been to only take cod over an agreed size to allow stocks to replenish from younger fish.

So, codfish have responded to this selection pressure by becoming sexually mature earlier before reaching the size at which they would previously have become sexually mature. Under this intense selection pressure, evolution that would normally be expected to take hundreds of thousands or millions of years, has occurred in a few decades.

This discovery was made by Brendan N. Reid, and Malin L. Pinsky of the Department of Ecology, Evolution, and Natural Resources, Rutgers University, NJ, USA, and Bastiaan Star of the Center for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, Norway, using new techniques that enabled them to extract DNA from codfish caught more than 110 years ago, and analyse it with sufficient sensitivity to detect subtle changes over time when compared with that of recent samples.

It transpired that the evolution involved changed to multiple genes, and these changes were seen in fish from both sides of the Atlantic.

As the Rutgers University news release explains:

The overfishing of codfish spanning the second half of the 20th century indicates that human action can force evolutionary changes more quickly than widely believed, according to a Rutgers-led study.

Published in the Philosophical Transactions of the Royal Society B: Biological Sciences, a report by scientists offers the first genomic evidence that Atlantic cod evolved new traits over only decades during a period of overfishing – evolutionary changes that scientists formerly believed could take millions of years.

The discovery was made possible by new technology that allowed us to extract and read the genetic code of cod, some caught more than 110 years ago, as well as new analytical techniques that detect subtle changes in that genetic code.

Associate professor Malin Pinsky, senior author
Department of Ecology, Evolution and Natural Resources
Rutgers School of Environmental and Biological Sciences (SEBS).

Scientists had noted that many overfished cod, by the end of the 20th century, had developed what looked to be a survival advantage – maturing earlier and growing less large, making them less likely to be singled out to be caught and more likely to reproduce before being caught. Searches for transformations in key genes, however, turned out to be unsuccessful.

Undeterred, the researchers asked a different question. What if the changes were occurring in many genes at once, rather than a few? The insight, coupled with new technology, propelled the Rutgers-led team to make the discovery.

We have now been able to demonstrate that many genes throughout the genome did shift in the same way in cod from both sides of the Atlantic Ocean over the past 100 years. This suggests that cod did indeed evolve in response to fishing through small changes in many genes, something we didn’t have clear evidence for before in any overfished species.

Dr Brendan Reid, first author
Department of Ecology, Evolution and Natural Resources at SEBS.

Atlantic cod live in cold waters and deep-sea regions throughout the North Atlantic. Popular for their mild flavor and dense, flaky flesh, codfish is one of the most common ingredients in fish and chips. Cod livers are processed to make cod liver oil, a common source of essential vitamins.

In the 1990’s, Atlantic cod populations fell to 1 percent of historical levels, due to decades of overfishing. Starting in the 1970s, powerful trawlers equipped with advanced radar and sonar systems allowed commercial fishermen to collect cod from a larger area, and fish more deeply and for longer periods than ever before. Cod stocks, as a result, were depleted at a faster rate than could be replenished, ultimately leading to the fisheries’ collapse, and as the Rutgers-led research shows, its rapid evolution.

The new research insights offer hope for the possible re-emergence of the codfish population which has been slowly rebounding since fishing pressure has been reduced, the scientists said.

Since evolution in response to fishing happened through lots of small changes in many genes rather than large changes in one or two genes, and cod have maintained most of their genetic diversity, it will be easier for cod to evolve back towards their previous pattern of slower growth at large sizes. The fact that cod populations are rebounding and shifting back towards previous patterns of growth suggests, given proper management, this fishery can return to its previous state and provide a sustainable source of food for a large number of people and a source of income for coastal communities that heavily depend on fishing.

Dr Brendan Reid.

Details are given in the scientists' open access report in the Philosophical Transactions of the Royal Society B: Biological Sciences, as part of the Journal's theme issue ‘Detecting and attributing the causes of biodiversity change: needs, gaps and solutions’.

Figure 1. Map showing sampling scheme and divergence among populations (adapted from Pinsky et al. [38]). (a) Sampling locations and times. Distribution of Atlantic cod (dark blue) is shown based on UN FAO data (https://www.fao.org/fishery/geonetwork/srv/eng/catalog.search#/metadata/fao-species-map-cod). (b) Population assignment for each individual (with proportion of inferred ancestry Q shown as coloured bars) for Canada (1940 and 2013 samples) and Norway (1907 and 2014 samples) along with overall temporal and spatial F_ST values between these samples.

Copyright: © 2023 The authors.
Published by The Royal Society. Open access. (CC BY 4.0)

Abstract

Populations can adapt to novel selection pressures through dramatic frequency changes in a few genes of large effect or subtle shifts in many genes of small effect. The latter (polygenic adaptation) is expected to be the primary mode of evolution for many life-history traits but tends to be more difficult to detect than changes in genes of large effect. Atlantic cod (Gadus morhua) were subjected to intense fishing pressure over the twentieth century, leading to abundance crashes and a phenotypic shift toward earlier maturation across many populations. Here, we use spatially replicated temporal genomic data to test for a shared polygenic adaptive response to fishing using methods previously applied to evolve-and-resequence experiments. Cod populations on either side of the Atlantic show covariance in allele frequency change across the genome that are characteristic of recent polygenic adaptation. Using simulations, we demonstrate that the degree of covariance in allele frequency change observed in cod is unlikely to be explained by neutral processes or background selection. As human pressures on wild populations continue to increase, understanding and attributing modes of adaptation using methods similar to those demonstrated here will be important in identifying the capacity for adaptive responses and evolutionary rescue.

Reid, Brendan N.; Star, Bastiaan; Pinsky, Malin L.
Detecting parallel polygenic adaptation to novel evolutionary pressure in wild populations: a case study in Atlantic cod (Gadus morhua)
Philosophical Transactions of the Royal Society B: Biological Sciences 378: 20220190. DOI: 10.1098/rstb.2022.0190.

Copyright: © 2023 The authors.
Published by The Royal Society. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

In other words, detectable evolution in response to intensive but selective predation, and similar changes seen in different populations subject to the same selection pressure, just as the Theory of Evolution by Natural Selection predicts.

I can hear a chorus of creationists bleating, "But they're still codfish! So it's not evolution!", showing the world that they don't understand what biologists mean by evolution - change in allele frequency in a population of time - and have been fooled by their cult leaders into thinking evolution means one species changing into another, unrelated, species, such as a cat changing into a dog, a crocodile into a duck or a bacterium into a human.

Only by remaining stoically ignorant and pretending that that childish parody is what science refers to as 'evolution', so creationists have something to attack, because, as this paper shows, real evolution is observable and predictable to those who understand what the term means.

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Thank you for sharing!

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