There is something strange about the Solomon Islands, lying east of Papua New Guinea and northeast of Australia. The bats that inhabit the islands seem to have evolved in ways that are difficult to understand.
Before creationists get over-excited and think we've found an example of species that didn't evolve but were made by magic, the question is not whether they evolved, but how? The scientists are in no doubt that the process was an evolutionary one and show no signs of concluding that a supernatural entity was involved. The puzzle is that genetically distinct species on different islands, occupying the same niche, have evolved such a high degree of phenotypic convergence that they are almost indistinguishable, so were previously classified as the same species, although genetically they are not even close relatives. The question is what is it about the environment on these islands that has driven this high level of convergence.
Each of the islands in the archipelago has a population of bats, usually 3-5 species on each island, consisting of a small, medium and large species and on islands with four species, an extra-large. One island has five species so gets an extra small bat.
That all seemed fairly straightforward on the assumption that the five distinct species had each found a niche on each island, and they certainly looked identical when comparing the different sized bats on each island. However, that was before we had DNA sequencing techniques.
DNA analysis has shown that the large bats on different islands, although identical in appearance, are not closely related - they have converged on that appearance from different ancestral bats.
This was discovered by a research team of scientists from University of Melbourne, Australia, the University of Kansas, USA, Jame Cook University, Australia and others. Their work is published open access in the journal, Evolution (the National Journal of Organic Evolution). It is explained in a University of Kansas news release:
A study of body size in leaf-nosed bats of the Solomon Islands has revealed surprising genetic diversity among nearly indistinguishable species on different islands. The research team behind the study from the University of Melbourne, Australia, included several evolutionary biologists from the University of Kansas — who collected specimens in the field, conducted genetic analysis and co-wrote the research appearing in the journal Evolution.According to Moyle, who also serves as professor of evolutionary biology at KU, previous generations of researchers reviewed the bats’ morphology, or physical traits, and concluded they’re one species.This is genus of bats called Hipposideros with multiple species all over Southeast Asia in the Pacific. In the Solomon Islands, where we've been doing a lot of fieldwork, on each island there can be four or five different species, and they parse out in terms of body size. There's a small, medium, large — or if there's more than three species, there's a small, medium, large and extra-large. On one island there's five, so there's an extra small.
You go from one island to the next, and the medium-sized species is identical to the other islands. Biologists have always looked at those and said, ‘OK, it's obvious. There's a small, medium and large size species distributed across multiple islands.’
Professor Robert G. Moyle, co-author
Senior curator of ornithology
Biodiversity Institute and Department of Ecology and Evolutionary Biology
The University of Kansas, Lawrence, KS, USA.However, Moyle and his collaborators had more modern analysis at their disposal. In sequencing the DNA of bats they collected from the field (along with specimens from museum collections), the team found the large and extra-large bat species weren’t actually closely related.
Photographs from a Guadalcanal field site demonstrating the size difference between sympatric species H. diadema and H. dinops.
Credit: Lavery et al
The team performed precise measurements on bats from different islands, confirming previous work by scientists in the Solomon Islands.That means that somehow these populations arrived at this identical body size and appearance not by being closely related — but we usually think identical-looking things are that way because they're really closely related. It brings up questions like what's unique about these islands that you’d have convergence of body size and appearance into really stable size classes on different islands?
Professor Robert G. Moyle, co-author
Moyle’s collaborators included lead author Tyrone Lavery of the University of Melbourne and KU’s Biodiversity Institute and Natural History Museum. Other KU co-authors include Devon DeRaad, doctoral student, and Lucas DeCicco, collections manager, both of the Biodiversity Institute and Natural History Museum; and Karen Olson of both KU and Rutgers University. They were joined by Piokera Holland of Ecological Solutions Solomon Islands; Jennifer Seddon of James Cook University and Luke Leung of the Rodent Testing Centre in Gatton, Australia.All the large ones from different islands all clustered together in their measurements. It's not just that the earlier biologists made a mistake. They looked at them and said, ‘Oh, yeah, they're the same.’ And they're actually not. We measured them, and they're all clustered together, though they’re different species. We verified — sort of — that earlier morphological work.
Professor Robert G. Moyle, co-author
Genetic analysis that revealed the bats weren’t closely related was performed at KU’s Genome Sequencing Core.
DeRadd said the work could be “highly relevant” for conservation efforts in identifying evolutionarily significant units in this group.When we created family trees using the bats’ DNA, we found that what we thought was just one species of large bat in the Solomon Islands was actually a case where bigger bats had evolved from the smaller species multiple times across different islands. We think these larger bats might be evolving to take advantage of prey that the smaller bats aren’t eating.
Tyrone H Lavery, lead author
School of BioSciences
The University of Melbourne, Melbourne, VIC, Australia.
According to DeCicco, the new understanding of leaf-nosed bats was fascinating on a purely theoretical level.Body size had misled the taxonomy. It turns out every island's population of extra-large bats is basically genetically unique and deserving of conservation. Understanding that is really helpful. There are issues with deforestation. If we don't know whether these populations are unique, it's hard to know whether we should be putting effort into conserving them.
Devon A DeRaad, co-author
Biodiversity Institute and Department of Ecology and Evolutionary Biology
The University of Kansas, Lawrence, KS, United States.
We study evolutionary processes that lead to biodiversity. This shows nature is more complex. We humans love to try to find patterns — and researchers love to try to find rules that apply to broad suites of organisms. It's super cool when we find exceptions to these rules. These are patterns that you see duplicated over lots of different taxa on lots of different islands — a large and a small species, or two closely related species that differ somehow to partition their niches. We're seeing there are lots of different evolutionary scenarios that can produce that same pattern.
Lucas H DeCicco, co-author
Biodiversity Institute and Department of Ecology and Evolutionary Biology
The University of Kansas, Lawrence, KS, United States
AbstractOnce again science refutes creationism by showing the close link between the environment and evolution, which is entirely consistent with the Darwinian model of the environment selecting for those variants best fitted to succeed within it, and those characteristics being inherited by descendants, so the population moves towards greater fitness in that selective environment.
Body size is a key morphological attribute, often used to delimit species boundaries among closely related taxa. But body size can evolve in parallel, reaching similar final states despite independent evolutionary and geographic origins, leading to faulty assumptions of evolutionary history. Here, we document parallel evolution in body size in the widely distributed leaf-nosed bat genus Hipposideros, which has misled both taxonomic and evolutionary inference. We sequenced reduced representation genomic loci and measured external morphological characters from three closely related species from the Solomon Islands archipelago, delimited by body size. Species tree reconstruction confirms the paraphyly of two morphologically designated species. The nonsister relationship between large-bodied H. dinops lineages found on different islands indicates that large-bodied ecomorphs have evolved independently at least twice in the history of this radiation. A lack of evidence for gene flow between sympatric, closely related taxa suggests the rapid evolution of strong reproductive isolating barriers between morphologically distinct populations. Our results position Solomon Islands Hipposideros as a novel vertebrate system for studying the repeatability of parallel evolution under natural conditions. We conclude by offering testable hypotheses for how geography and ecology could be mediating the repeated evolution of large-bodied Hipposideros lineages in the Solomon Islands.
Introduction
Radiations of closely related lineages, replicated across islands or lakes, have revealed much about the evolution of phenotypic variation (Bolnick et al., 2018; Heckley et al., 2022; Magalhaes et al., 2021; Schluter, 2000). Among the most striking patterns uncovered include species groups that have diversified in parallel, beginning at similar evolutionary starting points to independently arrive at similar endpoints (i.e., independently derived phenotypic similarity in two or more lineages) (Cerca, 2023; Losos, 2009; Magalhaes et al., 2021). Famous examples include Anolis lizards of the Greater Antilles (Losos, 2009; Mahler et al., 2013), Hawaiian spiders (Gillespie et al., 2018.1), Arctic charr (Adams et al., 2008), and benthic and limnetic pairs of sticklebacks (Schluter, 2000). These and other examples of phenotypic parallelism have provided strong lines of evidence for the roles of natural selection, environmental variation, and vacant ecological niches in spurring speciation (Stuart et al., 2017).
Body size is a fundamental morphological trait that features prominently among the phenotypic changes that accompany parallel radiations (Adams et al., 2008; Boughman et al., 2005; Kozak et al., 2009.1; Nagel & Schluter, 1998; Ratciliffe & Grant, 1983; Richmond & Reeder, 2002). It is also a critical variable that influences almost every life history characteristic of an organism, including prey opportunities, risk of predation, ability to thermoregulate, and dispersal ability (Gardner et al., 2011; Jenkins et al., 2007; Sinclair et al., 2003). Interspecies differences in body size can also act as a premating reproductive isolating barrier, playing an important role in mate recognition and contributing to long-term genetic isolation (Nagel & Schluter, 1998; Ratciliffe & Grant, 1983). For these reasons, measurements of body size are often used to delimit species boundaries among closely related taxa (e.g., Chen et al., 2017.1; Venkatraman et al., 2019). However, taxonomic and evolutionary inferences drawn from body size alone can be misleading and mask more complex underlying histories (e.g., DeCicco et al., 2020; Richmond & Reeder, 2002).
Leaf-nosed bats (genus Hipposideros Gray, 1831) are a lineage of insectivorous bats distributed through much of the Old World tropics and organized into nine species groups (Hill, 1963; Simmons, 2005.1). The diadema species group includes H. diadema Andersen, 1905, recognized as a single widespread species occurring from Southeast Asia, through the Philippines, New Guinea and into northern Australia and the Solomon Islands. Other members are largely restricted range endemics (e.g., H. inexpectatus Laurie & Hill, 1954; H. inornatus McKean, 1970; H. pelingensis Shamel, 1940; H. dinops Andersen, 1905; H. demissus Andersen, 1909) (Hill, 1963). In the Solomon Islands archipelago H. diadema is distributed across all larger central islands, except for Makira, which supports a smaller-bodied population that has been split off as the endemic Makira Leaf-nosed Bat (H. demissus). The Solomon Islands endemic fierce leaf-nosed bat (H. dinops) is endemic to the archipelago and occurs in sympatry with H. diadema from Bougainville to Guadalcanal and Malaita (i.e., excluding Makira) (Lavery & Flannery, 2023.1; Figure 1A and B).
Phylogenetic reconstructions based on DNA sequence data for the Family Hipposideridae recovered Solomon Islands H. diadema, H. dinops, and H. demissus interspersed throughout a single, poorly resolved clade (Lavery et al., 2014). Shallow genetic divergence raised questions about the taxonomic validity of H. dinops and H. demissus. But most puzzling was a well-supported case of reciprocal paraphyly, whereby two mitochondrial clades each contained sister pairs of H. dinops and H. diadema. Further, mitochondrial divergence values between H. diadema samples from the Solomon Islands and New Guinea were greater than any observed divergence values between H. diadema and H. dinops samples from within the Solomon Islands (Lavery et al., 2014). These unexpected relationships suggested the rapid and repeated evolution of larger-bodied Hipposideros ecomorphs on separate islands in the archipelago and that the taxonomic arrangement based on body size did not correspond with the evolutionary history of this group. Here, using expanded sampling and both morphological and genomic datasets, we aimed to further resolve the taxonomy and evolutionary history of the Solomon Islands H. diadema/dinops complex. We posed three key questions: (1) Can standard body size measurements be used to assign individuals to described species confidently? (2) Do thousands of genome-wide markers reaffirm reciprocal monophyly among species identified by body size? (3) Has gene flow ceased between recently diverged populations, indicating the evolution of genetic isolating barriers between sympatric taxa?Figure 1.
Solomon Islands Archipelago Hipposideros: (A) known distributions of these three species in the Solomon Islands and extralimital distribution of H. diadema (inset); (B) photographs from a Guadalcanal field site demonstrating the size difference between sympatric H. diadema and H. dinops; and (C) a boxplot of forearm lengths recorded from 20 H. demissus (Makira), 54 H. diadema (Bougainville, Choiseul, Guadalcanal, Malaita, Ngella, and Santa Isabel), and 29 H. dinops (Bougainville, Gatokae, Guadalcanal, Malaita, and Santa Isabel).
Tyrone H Lavery, Devon A DeRaad, Piokera S Holland, Karen V Olson, Lucas H DeCicco, Jennifer M Seddon, Luke K P Leung, Robert G Moyle
Parallel evolution in an island archipelago revealed by genomic sequencing of Hipposideros leaf-nosed bats Evolution, 2024;, qpae039, https://doi.org/10.1093/evolut/qpae039
Copyright: © 2024 The authors.
Published by Oxford University Press. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
And that, in a nutshell, is evolution by natural selection.
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Bats are fascinating in their biology and behavior, and like frogs, they reflect how healthy or how unhealthy the ecosystem is. If a place has numerous healthy bats and frogs then it's a healthy ecosystem. On the other hand if a place has dwindling number of bats and frogs, or no bats and no frogs, or sickly bats and frogs, then that's a worrying sign that the ecosystem is in trouble.
ReplyDeleteThe Solomon Islands are afflicted with many of the serious problems which are found all over the world. First are the evils inflicted by humans such as deforestation, logging, pollution, and crime. Then there are the miseries from Nature such as dangerous, deadly animal life, volcanoes, typhoons, cyclones, droughts, flooding, unclean water, lightning strikes, tsunamis. The Solomon Islands has a serious problem with malaria and there's a venomous Centipede which has a bite that's one of the worst pains known to man. It's more painful than many kinds of venomous snakes. It's as painful or worse than kidney stone. That's extremely scary. The Solomon Islands are also rumoured by some scientists to be in danger of sinking beneath the waves in the future.
Other islands that have been spoiled and ruined by humans and spoiled and ruined by Nature are the South Pacific islands of the Marquesas, Tahiti, Samoa, Fiji, the Cook Islands, and the Tonga islands have been ruined by nuclear fallout, and in the North Pacific, nuclear testing has ruined the Micronesian islands. Nuclear fallout has spread hundreds of miles to places such as Guam. The lovely island of Guam in the North Pacific and the lovely island of Tahiti in the South Pacific have been ruined by nuclear fallout causing a higher cancer rate.
Many other islands are afflicted with volcanoes, malaria, dengue fever, centipedes, and the Kiribati islands are predicted to be the first islands to sink beneath the waves in the future. The Hawaiian islands have volcanoes, vog, acid rain, and pollution from motor vehicles. There is no paradise anywhere on earth.