The Darwin Diaries #2: Los Insectos de Quito

“We see the great law of homologous structures in the construction of the mouths of insects: what can be more different than the immensely long spiral proboscis of a sphinx-moth, the curious folded one of a bee or bug, and the great jaws of a beetle?—yet all these organs, serving for such different purposes, are formed by infinitely numerous modifications of an upper lip, mandibles, and two pairs of maxillæ.” -Charles Darwin, On the Origin of the Species

When entering the Bellavista Cloud Forest your first impression of the natural landscape are the large organisms and structures: the plants, the mountains, and of course the clouds. However, as I hiked along the path straggling in the back of the group I started to notice the ‘micro-world’ of this system, specifically the insects and arachnids. While examining these individuals I noticed them doing many different things: pollinating, mating, and engaging in herbivory and a quote from On the Origin of Species popped into my head. Darwin used insects as an example when discussing the principle of homologous structures and as I walked around the cloud forest I began to understand his point. Insects have a wide range of structures for the appendages they use to consume, reproduce, and pollinate and yet they all evolved from an original simplistic structure. The amount of diversity of these proboscises, antennas, and mandibles is astounding and it’s hard to believe these individuals are somehow closely related evolutionarily.

Beetles:

The insect group of beetles were extremely abundant in the Cloud Forest and almost all of them were found on plants that had signs of herbivory indicating that they may be the main source of plant consumption in the system. When looking at all of the different types of beetles I observed their similarities and differences are obvious. All of the beetles have the same shape of antennas indicating that they all use them for the same function (most likely navigation and sensing). They also have the same body shape and thick exoskeleton which indicates that their structure evolved due to many advantageous mutations for their particular niche. Something that is very different about them is color: black, green, blue, yellow, and red seem to be the most common color for this family of insects, however shapes and shine seem to be very species specific. Some have color separating body parts (the yellow head and black body), some have spots (the green beetle with black spots and the black beetle with red spots), and some are iridescent where as others are opaque. These qualitative differences between species is most likely due to reproduction, having a unique color/texture that other individuals can recognize and be attracted to ensures speciation and avoids hybridization of species.

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Bees and Wasps:

I was lucky enough to find some bees and wasps during the hike and I observed something very interesting about them: we often associate them together most likely due to their physical similarities despite the fact that the often have completely different life histories and roles in ecosystems. You can’t deny that they look similar: they both have a clearly segmented body that ends in a pointed thorax, long legs, large window pane like wings, and of course stingers. However, most wasps are parasitoids and most are not pollinators, whereas bees are the definition of pollinators and do not rely on other organisms to complete their life cycles. This wasp in particular uses it’s long proboscis to insert its eggs into the bodies of burrowing beetles, whereas this bee uses a similar structure to transport pollen. As far as ecosystem structure the wasp is a predator/parasite of other insects whereas the bee is necessary for plant reproduction. In short, despite their appearances one is a pillar of the community and the other is a hardened criminal.

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Butterflies and Moths:

Butterflies and moths, much like wasps and bees, look extremely similar structurally: they both have long antennas that end in a point, four individual wings that attach at the body, and proboscises that allow them to collect nectar and pollen from plants. The main difference between them physically is their different strategies in allocation of energy to pigmentation. Butterflies are known to be extremely colorful with intricate patterns, whereas the moth is usually regarded as their ugly step sister. So why did these two groups diverge to have very different patterns? One possibly theory is that competition amongst Lepidoptera species led to some becoming nocturnal (moths) and some being active during the day (butterflies). Because of this difference in time of activity they have evolved different adaptations.

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Caterpillars and Centipedes:

It was a very special treat to find these guys, and though they may look like sticks, they’re actually insects. The picture on the left showcases a very special caterpillar, if you can’t find it you’ve been tricked like many of their prey. It’s standing straight up on the white flower attempting to disguise itself as an innocent piece of plant until a yummy meal comes along. The centipede is easier to see, chilling in the shade under a large leaf. Both of these insects look very different from the rest, most likely due to the absence of wings. Though they look very similar any kindergartner can tell you that one is a precursor to its final form of a butterfly/moth and the other is a full-fledged adult. Only certain kindergartners may know this, but they also have very different diets, one is a carnivore (the caterpillar is a moth species Eupithecia sp.) and the other is an herbivore.

These two individuals are interesting to compare because they are flightless for very different evolutionary reasons: the caterpillar is simply an immature form and they will develop wings after the pupal stage. This makes sense as an evolutionary strategy as the larval form of the insect must allocate all its energy to growth and metamorphosis, wings are an unnecessary feature until the organism starts to focus on reproduction or migration. Having wings while reproducing is a great strategy as it allows the organism to disperse their young in a variety of habitats ensuring the survival of the species.

The centipede is a different story; I have come up with two possible hypotheses for why these insects are flightless: a primitive ancestor that never evolved wings, or an ancestor that had wings but then lost them over time. The first hypothesis makes the most sense for the centipede as it’s many legs allows it to move quickly, it’s diet consists of stationary plants, and it is not a pollinator, all of these qualities have resulted in no evolutionary pressure to evolve wings. However, in the case of the secondary hypothesis perhaps the centipede’s ancestor had wings but a mutation occurred in the population which made them smaller or non-functional, if this mutation was advantageous or neutral it would make sense that over time the centipede would become wingless.

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Flies, Flying Beetles, and Crickets:

When examining crickets and flies I began to think about the evolution of insect legs, specifically about the potential tradeoff between strong legs and large wings. As you can see in the picture below the cricket (left) has large and powerful back legs which allow it to jump, however, like we discussed earlier the wings of a cricket are either small, non-existent, or used for alternative purposes (like mating calls). The fly all the way to the right has a very large body to wing ratio, however their legs are very small. The middle picture represents a flying beetle with medium back legs and medium wings. From my very limited observations I have to wonder if this is a general trend with most insect species.

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Cricket= big legs + small wings, Flying Beetle= medium legs + medium wings, Fly= small legs + big wings

Chucky D Bonus:

Darwin was a total insect nerd, his first science gig in university was assisting an entomologist and Darwin would eventually become Vice-President of the Entomolgical Society of London. Darwin didn’t have a fancy camera, he had to draw the insects he saw, here are a few:

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