Madrid, 21 (Europe Press)
Human activity is currently causing a loss of natural diversity that some experts are calling the sixth mass extinction event in Earth’s history. The decline of insects is particularly worrisome: not only are insects a very diverse group of creatures in their own right, they are also of enormous ecological and economic importance.
The extent of insect disappearance can only be described as exceptional. Therefore, to better understand the underlying processes, it is worth delving into past extinction events: some insect groups gained importance and diversified, while others passed through and were forced to retreat into the few remaining niches.
This last point seems to have been the case for the lepidoptera, whose modern representatives include the lepidopterans and antelopes. Researchers have long suspected that the importance of this group of insects tends to decline since prehistoric times. To date, however, there has been no quantitative validation of this hypothesis.
Now, a team working with biologists Professor Caroline Haug and Professor Joachim Haug of LMU (Ludwig-Maximilians-Universität München) has published a study in Scientific Reports that documents the diversification of neutrophils from the Cretaceous period to the present day. For the first time, statistical analysis supports scientists’ view of these insects through evolutionary history.
But how do we measure and compare insect biodiversity over the course of evolution? At best, we can only paint an incomplete picture of a small fraction of the biodiversity that was dominant in ecosystems in the past, because insect fossils are so rare. And while Jurassic Park may have fueled expectations to the contrary, DNA can no longer be extracted for use in ancestry analysis from the fearsome, amber-coated crawler during the Cretaceous period, LMU reports in a statement.
Neuroptera are dead insects, the larvae of which are very different in appearance and lifestyle from adults. While many nepidoptera pollinate flowers after metamorphosis, their larvae are often voracious predators, as evidenced by their strikingly patterned mouthparts. It was precisely these mouthparts of the larvae that were the focus of the researchers. “Unfortunately, the larval stage is often neglected in such analyses,” says Joachim Hough. “However, larvae in particular often display morphological features that we can use as a very useful database.”
The basic idea is simple: different shapes are a sign of biodiversity. The more different head shapes and patterns present in neuroptera larvae, the more ecological functions these creatures perform. It follows that if an exceptionally large variety of head and mouth parts occurred in a given geological period, it is reasonable to conclude that these insects occupied many different niches at that time. The principle is valid even if only a few specimens survive and the relationship remains unclear.
The researchers measured the heads of more than 1,000 caterpillars, including nearly 300 fossilized neuroptera caterpillars known worldwide and 800 specimens still alive today. In this way, they were able to confirm that the diversity of Neuroptera larvae has indeed declined over the past 100 million years.
“Although our view of the past is limited to a small sample size and very specific regions around the world, we are able to detect greater morphological diversity among Neuroptera larvae of the Cretaceous period,” says Caroline Hauge. “So it’s possible that the actual diversity was much higher in the past.” However, the big picture of the history of Neuroptera is complex: while its diversity as a whole has certainly declined, some lineages of Neuroptera have diversified and thus gained importance.
“Our work also showed how much potential there is in the morphological study of insect larvae,” adds Caroline Hogg. “Quantitative morphology can reveal changes that cannot be recorded quantitatively within a taxonomic framework.”