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The Bee

A Natural History

PRINCETON UNIVERSITY PRESS

Evolution & Development

EVOLUTIONARY PUZZLES

Charles Darwin was fascinated by bees. He considered eusocial ("truly" social) insects such as bees, wasps, ants, and termites to be evolutionary puzzles. The idea that individuals would forgo reproduction to serve a dominant individual (a queen) who is the only reproducing female in the colony was a threat to his theory of evolution by natural selection. Even now, when we understand that evolution relies on individuals passing their genes on to the next generation, it is a puzzle. If organisms do not reproduce, their genes will not be passed on, so this sterile behavior should not persist. But it does. How can individuals that give up reproduction be favored by natural selection? Furthermore, why are these social insects so successful? Some of the answers to these puzzles can be found in Chapter 2.

THE EARLIEST BEES

Over 100 million years ago, the world knew nothing of bees. Dinosaurs walked the earth, while wasps buzzed and flitted about, visiting fern-like plants to prey on smaller insects. In time, however, there was a change in the foraging preferences of some wasps. One particular lineage (the apoid wasps, such as digger wasps, mud dauber wasps, and thread-waisted wasps) began to abandon hunting for animal protein in favor of a vegetarian lifestyle based on flowers. Thus, bees are descended from carnivorous wasps, and over the course of countless generations they evolved to rely entirely on the tantalizingly sweet nectar, rich in carbohydrates, and the protein-rich pollen offered by the flowers as a reward to their pollinators. To attract the pollinators, flowering plants in turn developed attractive, scented, and brightly colored flowers, as flowers and bees co-evolved, one inadvertently helping the other.

EVOLVING ALONGSIDE FLOWERS

What makes bees so remarkable is their deeply ingrained relationship with flowers. The spread of flowering plants (angiosperms) across the world coincided with the appearance of the first bees, and together the two very different life forms each facilitated the diversification of the other. Slight changes in the genetic code of a plant species would favor a subset of bees, and vice versa. This co-evolution is a form of adaptive radiation, whereby a single ancestor species spreads out through its progeny into many descendant species, resulting in a blossoming of species diversity—in this case, a wide variety of different species of bees and flowering plants.

Early bees resembled their carnivorous wasp cousins, and had short tongues and sleek bodies. As bees evolved they developed longer tongues that could reach deep down into the hearts of even the deepest flowers to obtain the nectar. Some flowers developed longer flower tubes that only certain species of bees could utilize. Bees' bodies became hairy, enabling the more efficient collection of pollen, and some, including honey bees, developed specialized structures such as pollen baskets and brushes. Some bees today show stunning examples of specialization.

Honey Hunting & Beekeeping

Early humans relied on hunting wild animals and gathering vegetables and fruits, and in the course of their hunter-gatherer lifestyle they would have come across honey in bees' nests high in the trees. Bees provided our ancestors with perhaps their first condiment—honey. This complex concoction was alluring, and the desire for it drove men to work in groups to capture the golden prize. Their stories are documented in art, and cave drawings from the late Stone Age show a deeply rooted association between humans and bees. Artworks dating back as long ago as thirteen thousand years depict amazing feats, with men scaling seemingly impossibly tall trees, risking falls and stings, to pass the sweet comb down to helpers below. At first, this bravery was the only way of harvesting honey, and it was several thousand years before the refined practice of beekeeping was developed.

ANCIENT EGYPT

The earliest known human-constructed beehive, believed to be some three thousand years old, was discovered in Israel—but the Ancient Egyptians were the first known beekeepers. Evidence from cave drawings in Egypt reveals a long history of beekeeping, dating to at least 2400 BCE and thought to go back as far as 5000 BCE. At first the Egyptians relied on wild bees' nests, but their beekeeping practices later became very advanced. Not only did they construct beehives in the form of woven baskets covered in clay, which stayed permanently in one location, but they also used migratory hives, which floated down the River Nile on rafts, producing unique blends of honey as the bees visited the ever-changing riverside flowers. Egyptians favored the honey bees that were the best honey producers in the local environment, and through a process of artificial selection they gave evolution a helping hand to produce a new subspecies, the Egyptian honey bee (Apis mellifera lamarckii).

Some of the beekeepers were likely a lower class of workers, who were forced to work with these aggressive bees and return glorious honey to their superiors—and eventually to the pharaohs and the gods. Official guards accompanied other honey harvesters as they explored deep into the surrounding land, searching low-lying bushes and tall trees for wild hives.

AMERICA

The people of Mesoamerica (Mexico, Belize, Guatemala, El Salvador, Costa Rica, Honduras, and Nicaragua) kept stingless bees for some two thousand years before Europeans brought the western honey bee to their shores. There are likely at least 250 species of stingless bee in Brazil and at least 4,000 bee species native to North America alone, but the western honey bee is not native to the Americas.

The practice of beekeeping with honey bees was introduced to the New World by Europeans in the seventeenth century as a means of sustainable food production. Some honey bee colonies escaped from their beekeepers' management, and flew off into the woods in this unexplored new land. Native Americans named these feral honey bees "white man's flies," as their arrival announced the advance of the settlers, and gave warning of the inevitable conflict over land that lay ahead.

The Different Bee Groups

The global abundance of flowering plants from about 100 million years ago opened up a world of opportunity for the vegetarian wasps we now know as bees. Adaptive radiation proliferated across the globe and different types of bees evolved, matching the wide variety of environments, habitats, and flowers.

The twenty thousand species of bees are classified in nine families, which can be divided into three broad groups according to the average length of the bee's tongue, or proboscis. The long-tongued bees sip nectar from deep within the floral chambers. The shorter-tongued bees tend to be more ancient, more closely resembling their carnivorous wasp ancestors.

SHORT-TONGUED BEES

1. Andrenidae Mining bees, found in temperate, arid, warm climates. Absent from Australia. Hairy. Wasp legacy visible in facial structure (eyebrow-like colored patterns, males with facial hair), which might be used for recognition of individuals, but Andrenidae have more advanced eyes. Nest in simple soil burrows, or in hives that require multimodal communication to achieve complex architecture.

2. Colletidae Plasterer bees, masked bees, yellow-faced bees, polyester bees. Typically Australian, with some species in South America and a few in North America and Europe. Unique two-part tongue is used to create remarkable nest burrows lined with smooth polyester secretions. Some transport pollen by swallowing and regurgitating it, rather than by carrying it outside their bodies like most other bees, while other Colletidae carry pollen on leg hairs. Can have large ocelli (simple eyes), helping them to see in dim light.

3. Stenotritidae Smallest family of bees. Australian. Similar to Colletidae, but with one mouthpart instead of Colletidae's distinctive two. Nest in burrows. Large and fuzzy.

AboveAshy mining bee

MEDIUM-TONGUED BEES

4–6. Dasyponaidae, Meganomiidae, and Melittidae Primitive families, the least changed of all bees since the split from wasps. Found mainly in Africa. Tend to be picky specialists concerning their food source, sometimes forgoing pollen for flower oils. The Dasypodaidae and Meganomiidae families have often been treated as subfamilies of Melittidae.

7. Halictidae Sweat bees. Worldwide. Often attracted to sweat. Small. Can be colorful. Sting. Nest underground in soil or sand. Highly social, with some kleptoparasitic (see Apidae, right), but there are also solitary Halictids. Their range of social systems makes them a fascinating group to use for studying the evolution of social living.

LONG-TONGUED BEES

8. Apidae Cuckoo, carpenter, digger, bumble, stingless, and honey bees. Worldwide. With or without functional ovipositor (sting). Solitary to eusocial, some even parasitizing other bees by stealing their resources (kleptoparasitism)—such as cuckoo bees, which lay their eggs on pollen collected by their host bees. Some make products that are used by humans.

9. Megachilidae Leaf-cutter bees, mason bees, orchard bees, carder bees. Worldwide. Named for the materials they gather to make their nests. Carry pollen in a specialized structure (scopa) on the belly rather than on hind legs or internally, limiting their ability to carry pollen efficiently back to the nest and thus requiring more frequent trips to flowers. Their behavior within the flower also covers them in pollen. Combined, these factors make them particularly effective pollinators.

The Evolution & Development of the Honey Bee

Honey bees are living fossils. They comprise the genus Apis within the otherwise extinct tribe Apini. Apis includes the well-known western honey bee (A. mellifera), as well as similar Asian species A. cerana, A. koschevnikovi, and A. nigrocincta. Other eastern species include the small A. andreniformis and A. florea, and the giant A. dorsata. Most honey bees originated in Asia, but recent insights from sequencing the genome of A. mellifera indicate that it evolved in Africa, and then spread at least twice into Europe. The honey bees are closely related to other members of the subfamily Apinae, which includes bumble bees, long-horned bees, orchid bees, and digger bees. Those bees have small nests with one to a few hundred individuals, whereas honey bees evolved to live in complex, multi-layered hives, specializing in the long-term storage of honey to feed tens of thousands of individuals.

THE BROOD CYCLE

The eggs of a honey bee look for all the world like grains of white rice. The queen bee lays just one egg in each cell in the brood comb, and after three days the eggs hatch into larvae—tiny wormlike creatures that are as white as snow. Worker bees feed the larvae, which in due course develop into pupae—mummy-like pharaohs that undergo metamorphosis while enclosed in the privacy of a capped cell in the wax comb, until each finally emerges, two weeks later, as a fully grown worker bee.

THE QUEEN

Just a few eggs are laid in specially constructed queen cells. These eggs are destined to become queen bees. The queen's DNA is no different from that of her worker-bee sisters; the only difference is environmental. Royal jelly is a secretion produced by the workers and fed to all larvae for a short time, but the queen is fed extra rations, enabling her reproductive organs to develop fully. Simply because of a change in diet, her life is changed forever. She will live for years, rather than a month, and she may lay several hundred thousand eggs over her lifetime, rather than none.

The queen bee is larger than the workers. She emerges from her cell soft and fuzzy and remains that way for a day or so, allowing her body to darken and harden, as all newborn bees must. Within a few days of emerging from her cell, she will take off on the first of up to three mating flights. She will fly high to find her mates in areas where drones congregate. Honey bee queens are notorious for mating with more males than possibly any other animal on earth—genetic analyses have shown up to 29 different paternal lines within one queen's hive. Once mated sufficiently, the queen becomes a slave to her hive, remaining in it for the rest of her life.

Wild Bees Worldwide

Bees are found in nearly all terrestrial habitats worldwide, except in Antarctica and on the most barren mountaintops. They seem to thrive in our own urban environments, as well as in the Arctic Circle, where they take advantage of a seasonal superabundance of flowers. One major distinction across all bees is their relationship to flowers, with some bees specializing on particular plant species while others are generalists. Bees also differ in their habitats, with different foraging and other behavioral traits associated with each habitat type. Another key difference is between tropical and temperate bees.

NEW WORLD BEES

The Western Hemisphere once contained massive and untouched land masses, ripe with diverse yet connected habitats. Left largely unexploited by humans until recently in evolutionary terms, these vast lands were saturated with an unimaginable diversity of flowering plants. The diverse flora of the Americas allowed for thousands of unique bee species to evolve that specialized on native flowering plants.

The tiny squash bees, Peponapis and Xenoglossa, both of which are members of the long-horned bee family Eucerini, limit their pollen and nectar foraging to squashes, melons, and pumpkins. So intertwined are these bees and flowers that squash bees may occasionally live inside the flowers, timing their activity according to when the squash flowers are open and closed.

The loosestrife bee (Macropis sp.) has an affinity toward loosestrife flowers, but because these flowers are not rich in nectar it must be more of a generalist, foraging for other sources of carbohydrates for a balanced diet. Others, such as the striking blue orchard bee (Osmia lignaria), have a catholic diet of whatever blooms happen to be in season.

OLD WORLD BEES

In Africa and Asia, as elsewhere, persistent threats from predators shaped the evolutionary path of bee behavior, most often by forcing bees to stay on the move rather than settle down and invest in a sedentary lifestyle. Tropical areas tend to host more predators than temperate climates, and these are the habitats where we note more aggressive bees and wasps today. The gentle bees got picked off, or selected out, a long time ago in evolutionary history, posing a selection pressure that favored more aggressive bees in tropical environments. However, as in the Americas, bees were able to diversify alongside the flowering plants, to find safe havens in all sorts of habitats, ranging from sub-Saharan Africa to Siberia and nearly everywhere in between.

The honey bees used for beekeeping by the Ancient Egyptians were notably aggressive, and likely gave rise to a need for humans to perform selective breeding to artificially promote more desirable traits, such as a lack of aggression and low rates of swarming—as noted in the more temperate honey bee races in Italy and Russia.

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Excerpted from The Bee by Noah Wilson-Rich, Kelly Allin, Norman Carreck, Andrea Quigley. Copyright © 2014 Ivy Press Limited. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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