Category Archives: Charles Darwin

Do Birds Have Teeth?

Snow Goose teeth tomia Gloucester Massachusetts ©Kim Smith 2015Snow Goose Beak and Tomia

If I had thought about the answer to that question when I was five, I would have said yes, most definitely. At that time, our family was living on a lake in north central Florida. A friend’s unruly pet goose chased me home, nipping my bottom all the way to our front stoop!

The jagged points in the serrated-edge jaw of the Snow Goose are not called teeth because teeth are defined as having an enamel coating. There is a special word for the points and they are called tomia. During the Mesozoic era birds had teeth. Over time, birds developed specialized beaks suited to their diets. Bird beaks do the job teeth and lips once did. The Snow Goose’s tomia are not as tough as teeth but are perfectly suited to slicing through slippery grass.

The super graphic below, found on wiki, illustrates types of beaks and how the different shapes relate to the bird’s diet and foraging habits.

Wiki Bird Beak Graphic copy

Silversword Alliance

Haleakalā Silversword

Photos Courtesy of Forest and Kim Starr

Director’s Series at the Arnold Arboretum ~ Last night I had the pleasure of attending Robert Robichaux’s splendid lecture Restoring Hawaii’s Marvels of Evolution, presented at the Hunnewell Building of the Arnold Arboretum. Especially fascinating are examples of adaptive radiation, in which a singular North American mainland plant arrived on the islands and evolved into an array of different species, exhibiting fantastic variation in form and habitat.

See related post What is Adaptive Radiation?

Haleakalā Silversword

Mr. Robchauxi gave detailed information on the restoration efforts of the Haleakalā Silversword (Argyroxiphium sandwicense subsp. macrocephalum), perhaps Hawaii’s most famous native flowering plant, along with providng examples of other silversword species and lobeliads.

Haleakalā Silversword

A relative of the sunflower, Haleakalā Silversword may live for several decades, however it is monocarpic, meaning once-flowering, after which it dies. Flowering usually occurs from June through October and the single stalk may contain as many as 600 heads with up to 40 ray flowers surrounding approximately 600 disk florets. Haleakalā Silversword is found only on the island of Maui. The plant’s common name is derived from the genera’s numerous sword-like succulent leaves, which are covered with silver hairs. Since May of 1992, the Haleakalā Silversword  has been considered a threatened species by the U.S. Fish and Wildlife Service.

The silversword alliance refers to an adaptive radiation of over 5o Hawaiian species in the composite or sunflower family, Asteraceae, Tribe: Madieae (genera Dubautia, Wilkesia, and Agyroxiphium), and also to the Hawaiian Silversword Alliance Project (HSA), an adaptive evolution study project that is a collaborative effort among scientists at multiple public, private, and government institutions.

Kingdom: Plantae

Order: Asterales

Family: Asteraceae

Genus: Argyroxiphium

Species: A. sandwicense

Subspecies: A. s. subs. macrocephalum

What is Adaptive Radiation?

One of the most striking evolutionary patterns observed is called adaptive radiation. To radiate means to spread outward; not in the sense of speading out physically, but referring to a species that diversifies (“spreads out”) and generates multiple daughter species.

From Biology Online: When Charles Darwin was in the Galapagos islands, one of the first things he noticed is the variety of finches that existed on each of the islands. All in all, there were many different species of finch that differed in beak shape and overall size. This is adaptive radiation and natural selection at work.

Darwin’s Finches

These finches, better known as ‘Darwin’s Finches’ illustrated adaptive radiation. This is where species all deriving from a common ancestor have over time successfully adapted to their environment via natural selection.

Previously, the finches occupied the South American mainland, but somehow managed to occupy the Galapagos islands, over 600 miles away. They occupied an ecological niche with little competition.

As the population began to flourish in these advantageous conditions, intraspecific competition became a factor, and resources on the islands were squeezed and could not sustain the population of the finches for long.

Due to the mechanisms of natural selection, and changes in the gene pool, the finches became more adapted to the environment, illustrated by the diagram below.

Adaptive Radiation in Darwin's Finches

As competition grew, the finches managed to find new ecological niches, that would present less competition and allow them, and their genome to be continued.

As indicated by the diagram above, the finches adapted to take advantage of the various food sources available on the island, which were being used by other species. Over the long term, the original finch species may have disappeared, but by diversifying, would stand a better chance of survival.

All in all, the finches had adapted to their environment via natural selection, which in turn, has allowed the species to survive in the longer term, the prime directive of any species.

See related post Silversword Alliance.

Follow this link to read more about rapid adaptive radiation in the species rich Heliconius butterflies (longwings or passion-flower butterflies).

Heliconius butterflies