Tiny treetop flowers foster incredible beetle biodiversity

Hundreds of beetle species seem to be specialists that feed only from small white flowers on trees.
Susan Kirmse, CC BY-ND

Caroline S. Chaboo, University of Nebraska-Lincoln

The Research Brief is a short take on interesting academic work.

The big idea

Biologists have long known that rainforest treetops support a huge number of beetle species, but why these canopies are so rich in beetle diversity has remained a mystery. New research by my colleague Susan Kirmse and me shows that flowering trees play a critical role in maintaining this diversity, and that beetles may be among the most diverse pollinators in the animal kingdom.

We carried out a one-year study in a remote part of the Amazon rainforest in Venezuela. We used a specially built crane to collect a total of 6,698 adult beetles representing 859 species. These were gathered from 45 individual trees of 23 different tree species.

We were surprised to discover that the majority of these beetles – 647, or 75.3% of species found – were living on flowering trees. In fact, 527 beetle species in 41 families were associated exclusively with flowers. Interestingly, the majority of these species – almost 60% – were exclusively found on trees that produce lots of small white flowers.

Overall, this discovery shows that flowering trees are likely among the most important drivers for maintaining the high diversity of beetles in rainforests. But this relationship goes both ways. Our study also suggests that beetles may be among the most underappreciated pollinators in tropical forests.

A tall metal structure emerging from the forest canopy in Venezuela.
Using a specialized crane, the team was able to collect beetles from the very top of the forest canopy.
Susan Kirmse, CC BY-ND

Why it matters

Tropical rainforests are the very heart of Earth’s biodiversity. They harbor about 65% to 75% of all terrestrial species, including the most tree species and the most insects.

After finding such a tight relationship between beetles and flowering trees, we wondered: How many beetle species could be involved in pollination in the Amazon? Our study found an average of 26.35 unique beetle species for every species of tree. With an estimated 16,000 Amazonian tree species, this suggests that there might be more species of flower-visiting beetles than any other insects on Earth, potentially surpassing by far the 20,000 species of bees and the 19,000 species of butterflies.

Our study shows that flowering tree species play an important role as diversity hotspots in tropical rainforest canopies. For policymakers and biologists hoping to preserve or restore rainforests, promoting the cultivation of trees and other plants – especially those with lots of small white flowers that beetles love – could help to maintain species-rich communities. Flowers are a very important resource, providing food and shelter for thousands of insects in addition to beetles. Thus, preserving plant diversity or selecting many different indigenous tree species for reforestation can enhance the diversity of insects.

An image of a iridescent green-blue beetle.
Beetles like the Griburius auricapillus are just some of the hundreds of species that can be found in treetops.
Susan Kirmse, CC BY-ND

What still isn’t known

Our research was the first to describe this tight relationship between beetles and rainforest trees, especially with trees that produce thousands of small, simple flowers. But how this association came to be is still unclear.

Many of the beetle species were found only on trees with this particular type of flower. The trees get an obvious benefit: pollination. But what specifically these trees offer to the beetles requires further study. The simpler flowers are easier for beetles to access, but is the appeal food, like petals, pollen or nectar? Or maybe a home to find mates or lay eggs for the young to grow?

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What’s next

To fight the worldwide rapid declines in insect diversity, researchers and conservationists must understand the ecological connections between insects and their food plants. Long-term studies, particularly in research plots like the one we used in Venezuela, allow researchers to collect layers of information that help unravel the complexity of diversity.

Yet such sites rely on political interest and stability. Political instability in Venezuela is preventing our fieldwork from continuing at the Venezuela plot.

While we can’t return to our study site in Venezuela, it is clear that researchers must work together to understand the mysteries of life on Earth. But biologists are racing the clock as large rainforests are destroyed forever.The Conversation

Caroline S. Chaboo, Adjunct Professor in Insect Systematics, University of Nebraska-Lincoln

This article is republished from The Conversation under a Creative Commons license. Read the original article.


Basking sharks travel in extended families with their own ‘gourmet maps’ of feeding spots, genetic tagging reveals


Catherine S Jones, University of Aberdeen; Leslie Noble, Nord University, and Lilian Lieber, Queen’s University Belfast

Picture the scene. Swimming off Scotland’s west coast during a summer holiday you notice a large dark shark nearly 10 metres long headed towards you. A prominent triangular dorsal fin cuts the surface, the powerful rhythmically beating tail driving it silently through the cloudy green depths. You’re transfixed by a cavernous mouth large enough to swallow a seal.

Musing this may be your last swim, it might be surprising to learn this leviathan of the deep is a harmless yet endangered gentle giant. It has little interest in humans, focusing on some unseen bounty of the warmer summer waters: zooplankton, the tiny creatures found near the surface of the ocean.

This is the basking shark (Cetorhinus maximus), once common off western Europe, feeding on the annual plankton bonanza of the European shelf.

Our recent study suggests holidaymakers and basking sharks have much in common. They make temporary forays into these higher latitudes, travelling familiar routes with extended family, feeding on local fare at well-known places visited on previous trips.

Areas supporting high densities of zooplankton are like tourist traps, drawing basking sharks from across the Atlantic in late spring and summer. Hundreds converge in inshore surface waters on the Scottish west coast, Ireland and Isle of Man.

Once hunted for its oily liver across all oceans, basking sharks in the the north-east Atlantic were primarily targeted, with more than 80,000 slaughtered in the second half of the 20th century. This earned the world’s second biggest fish (after the whale shark) a place on the International Union for Conservation of Nature´s Red List. A critical indicator of biodiversity, this catalogue of species under threat of global extinction makes depressing reading.

Saving our sharks

Conservation management of the basking shark demands knowledge of its ecology and movement patterns. These slow-swimming coastal predators easily traverse the equator and ocean basins, moving from one legislative domain to another. Identifying important feeding sites and routes popular for annual migrations can therefore help countries enact effective protection.

Difficult to track and observe, satellite tagging has revealed shark movements, showing use of the ocean throughout a year. One study suggests that basking sharks have an attachment to particular areas, returning annually to feeding sites, a behaviour known as seasonal site fidelity.

Such localities are candidates for protection, designated Marine Protected Areas (MPAs), and ensure sharks remain undisturbed during sensitive and important life stages. But tagging informs us mainly about individual movements, leaving crucial conservation questions unanswered.

Our study focused on developing genetic markers to identify individuals and establish their migration routes, population connectivity and size. We also wanted to explore basking sharks’ genetic diversity – an indicator of a species’ ability to future proof against environmental change, and kinship of feeding clusters.

But developing tools removed only one obstacle. Another was lack of routine DNA sampling of basking shark groups. A breakthrough came when, in desperation, we discovered skin mucus from a tail swipe against a boat was a DNA source. Routine swabbing of basking shark groups – quickly and with minimal disturbance – provided genetic profiles of more than 400 individuals and a snapshot of those travelling together.

This register identified individuals arriving at summer feeding sites, revealing that sharks were re-sighted within seasons and again in later years, sometimes around the same date at sampling locations only kilometres apart. This supports findings of basking sharks repeatedly visiting feeding sites in the recently designated Sea of the Hebrides MPA. Ominously, our study also indicates the Irish Sea is an important migration route – an area of increasing human activity.

The dorsal fin of a basking shark breaking the surface of the sea.
The distinctive dorsal fin of a basking shark off the coast of Scotland.
Lilian Lieber, Author provided

Family ties

We expected the roaming and mixing of cosmopolitan, filter-feeders that live long lives to erode genetic differences between populations. But regular sampling of feeding groups revealed basking sharks off the coast of Ireland in spring (perhaps having wintered near the US) were genetically distinct from north-east Atlantic populations. This differentiation was explained when genetic snapshots made up family albums.

We found that basking shark groups consist of related individuals, indicating a tendency to travel prescribed seasonal migration routes as extended family parties. It would seem the family that feeds together, stays together.

Cetaceans often travel as kin groups, perhaps facilitating learning of migration routes and encouraging cooperative behaviours. This could mean that basking shark groups also exhibit complex behaviours. Certainly, they don’t fit the lone shark stereotype.

Until our study, the perception was that they moved into warmer waters from widespread locations, sniffing out a plankton meal, collecting as groups of unrelated individuals – like gourmands headed into the city, chancing on finding a good restaurant by smell.

Now it looks like basking sharks carry “road maps” of gourmet venues, taking the family along. Perhaps travelling together allows young kin to learn accurate navigation, and maybe many noses are better at sniffing out a meal of densely packed zooplankton.

Conservation biologists fret about genetic variation of threatened species. Large marine creatures have low rates of reproduction and consist of small populations. This means they accumulate genetic variation more slowly than the tiny, populous, rapidly reproducing plankton they eat. That lack of evolutionary currency slows responses to environmental change. In an important conservation milestone, our genetic estimates suggest a north-east Atlantic basking shark population not exceeding 10,000 individuals.

Worse still, most variation is distributed amongst families, so loss of kin groups erodes genetic variation rapidly – as when basking sharks were hunted, and as occurs now during accidental bycatch, when fishing vessels trap unwanted marine creatures in their nets.

Such population size and structure, coupled with tendencies to frequent inshore feeding areas earmarked for development of marine renewables such as windfarms, may not produce a happy outcome without intelligent management of such environments.
When it comes to basking shark conservation we have to remember that in a rapidly changing world, family matters.The Conversation

Catherine S Jones, Senior Lecturer, Biological Sciences, University of Aberdeen; Leslie Noble, Professor of Aquatic Biosciences, Nord University, and Lilian Lieber, Research Fellow in the Bryden Centre, School of Chemistry and Chemical Engineering, Queen’s University Belfast

This article is republished from The Conversation under a Creative Commons license. Read the original article.