Spectrum Biology - September 2016

 The canine teeth of wolves are specialised for ripping food.

 Herbivores, viz., deer have predominantly grinding

teeth. The front teeth of a beaver are used for chiseling

trees and branches. The elephant has two of its upper, front

teeth specialised as weapons and for moving objects.

 Omnivores, such as humans, pigs, bears, racoons have

teeth that can perform a number of tasks like tearing,

ripping, chiseling and grinding.

Slimmer’s Disease

Some body fats are essential for health, but a few individuals develop an

aversion to food and take steps to reduce their weight. The conditions

known as anorexia nervosa and bulimia nervosa. In anorexia, deliberate

dieting and sometimes deliberate vomiting, lead to serious weight loss and

even the loss of menstrual cycles. Patients have an obsessive fear of gaining

weight or becoming fat. They see themselves as much fatter than they

actually are. In bulimia, periods of excessive eating, i.e., binge eating are

followed by self-induced vomiting and use of laxatives to achieve weight

control. In this disease, patients do not necessarily lose excessive weight

and their menstrual cycles remain normal.

Salivary Glands

 Most fishes lack salivary glands. Lampreys are an exception

because they have a pair of glands that secrete an

anticoagulant needed to keep their prey’s blood flowing

as they feed.

 Some snakes have modified salivary glands that produce

venom, which is injected through fangs to immobilise prey.

 In amphibians and reptiles, salivary glands are lacking as

the secretion of oral digestive enzymes is not an important

function in them.

 Birds also do not possess salivary glands, while all

mammals have them.

Oesophagi

 The oesophagus is short in fishes and amphibians.

However, it is much longer in amniotes due to their longer

necks.

 Grain and seed eating birds have a crop that develops from

caudal portion of oesophagus. It is a storage structure that

allows birds to quickly ingest large quantities of locally

abundant food. This structure allows birds to reduce the

frequency of feeding and still maintain a high metabolic

rate.

Pigeon’s Milk

Pigeon’s milk is produced by the degeneration of the epithelial cells lining

the crop, under the control of prolactin hormone. This hormone is secreted by

the anterior lobe of the pituitary gland. This hormone stimulates and controls

the formation of pigeon’s milk. It (pigeon’s milk) contains water (65-81%),

protein-casein (13.3-18.8%), fat (6.9-12.7%) and lactose (1.5%). It is more

nourishing than the cow’s milk. Pigeon’s milk contains 35% of fat in

comparison to 3-5% in cow’s milk. The young ones fed on it double their

weight in two days. The pigeon’s milk is regurgitated to the youngs.

Stomachs

The stomach is considered as an ancestral vertebrate

structure. It evolved as vertebrates began to feed on

larger organisms that were caught at less frequent

intervals and required storage.

Specialised Structures of Stomach :

Giz zard

 Some fishes, some reptiles such as crocodilians and all

birds have a gizzard for grinding up food.

 The bird’s gizzard develops from the posterior part of

the stomach called the ventriculus. Pebbles that

have been swallowed are often retained in the gizzard

of grain-eating birds and facilitate the grinding

process.

Four New Species of Ants Discovered – Two

Named after ‘Game of Thrones’ Dragons

A group of Japanese entomologists has described and named

four new species of the ant genus Pheidole from the tropical

rainforests of Papua New Guinea and the Fijian islands.

Pheidole is a highly diverse genus of ants, with over 1,000

species recognized so far. The genus has the common name of

‘big headed ants,’ as Pheidolesoldier ants usually have huge

heads and jaws to break up large food items.

Amongst the Pheidole ants, the scientists discovered two new,

highly adorned, dragon-like species – P. viserion and

P. drogon — with distinctive large spines protruding from

their dorsal plates.

The scientific name of Pheidole drogon refers to Drogon, the

black-colored dragon of Daenerys Targaryen, a fictional

character from the George R. R. Martin’s novel ‘A Song of Ice

and Fire’ and TV series ‘Game of Thrones.’

Liver

Oesophagus

Crop

Proventriculus

Intestine

Cloaca

Pancreas

Digestive system of a pigeon

Ventriculus

(gizzard)

BIOLOGY