Biodiversity

Thursday, May 04, 2006

WHAT HAS GILLS AND A HEAD LIKE A CROCODILE?

A new fossil has been found in Canada, that might shed more light on the evolution of 4-legged land animals... If you are interested go to:

http://evolution.berkeley.edu/evolibrary/news/060501_tiktaalik

and find out more! Truely interesting stuff!


Karen Marais
BCB Hons NISL student
University of the Western Cape
Private Bag X17
Bellville

E-mail 2657211@uwc.ac.za

Web http://brit-journal.com/karen2006bcbnisl/

ADAPTIVE RADIATION: THE LEMUR WAY

Lemurs have been isolated on the island of Madagascar for millions of years and thus adaptive radiation of these creatures has been confined to this island. (1) The fossil record is poor and when exactly the lemurs inhabited Madagascar and when they split from the other prosimian primates would be guesswork, but the fact that Madagascar has been isolated for millions of years, is widely accepted. (1) The lemurs thus have had a long time to adapt to the different environments of the island and in the absence of other primates and relatively few mammals could fill many ecological niches, the island offered. According to Patricia Wright (1999, p. 31), “adaptive radiation of lemurs on Madagascar may have been uniquely characterized by selection toward efficiency to cope with the harsh and unpredictable island environment”. (2)

They differ from anthropoids (monkeys, apes, humans) in several behavioural features, such as female dominance, targeted female-female aggression, lack of sexual dimorphism, strict seasonal breeding and cathemerality (being active during the day as well as night). (2) There are several suggested hypothesis for these adaptations, the latest being the “energy frugality hypothesis” postulating that the majority of traits are either adaptations to conserve energy or to maximize use of scarce resources. (2)

In Africa and Asia other prosimians (bushbabies, pottos, lorises and tarsiers) remained small, solitary and nocturnal, avoiding the diurnal monkeys, to prevent competition. In Madagascar though, lemurs have a wide variety of lifestyles, varying degrees of social structures and they come in all sorts of sizes. One feature they still share with all other prosimians though, is their heavy reliance on their sense of smell. (3)

Some lemurs have become very small and fill a gap in the absence of squirrels and other prosimians. The smallest living primates today are the grey mouse-lemur (Microcebus murinus) and the rufous mouse-lemur (M. rufus) weighing only between 45-90 grams. (3, 4) They are nocturnal and generally solitary when foraging for food. During the day females sometimes group together sleeping in tree holes or nests built of leaves. (3, 4) They are also arboreal and their diet consists of fruit, flowers, nectar, insects and spiders. They have acute noses, which they use to detect food as well as keeping in touch with neighbours. They scent mark twigs by urinating in their cupped hands, wiping it on their feet and then wiping them on a branch, as well as leaving smelly footprints as they move on. (3) Some species of dwarf and mouse-lemurs even hibernate during the winter months, when food is scarce, which is very unusual behaviour for primates. (3)

In the genus Phaner there is a small lemur that has adapted to a specialized diet of resinous sap of certain trees. For this diet its adaptations involve teeth, tongue, nails and digestive system. (3)

The aye-aye (Daubentonia madagascariensis) must be one of the most unusual lemurs. They are nocturnal, about the size of a domestic cat and covered in a thick black fur coat with longer white-tipped hairs giving it a shaggy appearance. Their huge ears are capable of picking up faint sound of larvae inside wood. But it is their long bony third finger that is most remarkable. They move along in trees, tapping along with their fingers on wood and listening until they have found what they have been looking for; grubs! Their chisel-like teeth then quickly gnaw a hole in the wood and the long middle finger is then used to extract the grub. They also eat nuts and even eggs, again using their chisel-like teeth to gain access and then using their long finger to extract the content. (3, 5)

Probably the best known is the ring-tailed lemur (Lemur catta). They are also about the size of a domestic cat and inhabit the dry southern part of Madagascar. Their preferred habitat is the gallery forest that fringes major rivers, but they are found in other habitat as well. They are the best adapted to a partly terrestrial lifestyle of all the lemurs, although a lot of time is spent in the trees, where they mostly feed on fruit, but also leaves, seeds and the odd insect. These lemurs are diurnal and live in sociable societies that are led by females. Sent marking from glands on their wrists, armpits (males) and genital area (both sexes) is part of their daily routine and serves as territorial boundaries. (3)

Some lemurs make the most of both day and night and space out their activities over a 24-hour period. The brown lemur (Lemur fulvus) is one such specie. They mostly feed on fruit but also eat leaves. (3)

The family Indriidae contains the largest living lemurs, namely the indri (Indri indri). They are possibly the most strictly diurnal and arboreal of all lemurs. They live in small family groups and feed on leaves, flowers and fruit. They jump from tree to tree, usually hugging tree trunks, rather than flexible branches due to their weight. The indri is however famous for its singing. They use their eerie chorus to mark their territory. (3, 6)

The sifakas, like the indri are agile jumpers and can jump up to 10 meters. They are smaller than the indri and usually land upright. They do cover ground on the floor sometimes, but cannot walk on all fours, but will rather jump, with arms held high. (3, 6)

Some lemurs have become very specialized in their diet, like the golden bamboo lemur (Hapalemur aureus), the grey bamboo lemur (Hapalemur griseus) and the greater bamboo lemur (Hapalemur simus). What baffled scientists is that they all can all live together in close proximity eating from the same plants. It was then established that they prefer different parts of the same plant and so prevent competition. What is further remarkable is that the golden bamboo lemur prefers young bamboo shoots, containing cyanide and highly toxic, but this lemur has managed to overcome that obstacle. (3)

Today Madagascar has between 23-52 living species of lemurs (depending on the source one uses). (3, 8) But many more, especially the larger ones, have already gone extinct and due to continued habitat destruction and fragmentation, all remaining species are at risk. (3, 8)


References:

1. Martin RD. 2000. Origins, diversity and relationships of lemurs. International Journal of Primatology 21 (6): 1021-1049
2. Wright PC. 1999. Lemur traits and Madagascar ecology: coping with an island environment. American Journal of Physical Anthropology 110 (S29): 31-72
3. Preston-Mafham K. 1991. Madagascar. A Natural History. Pages 141-188, Chapter 7. The Lemurs. Cape Town. Struik Publishers.
4. Wikipedia contributors. Gray Mouse Lemur [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 9, 18:09 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Gray_Mouse_Lemur&oldid=47725424
5. Wikipedia contributors. Aye-aye [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 28, 05:04 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Aye-aye&oldid=50537743.
6. Wikipedia contributors. Indriidae [Internet]. Wikipedia, The Free Encyclopedia; 2006 Mar 24, 16:02 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Indriidae&oldid=45277136.
7. Wikipedia contributors. Golden Bamboo Lemur [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 27, 18:21 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Golden_Bamboo_Lemur&oldid=50456767.
8. Wikipedia contributors. Lemur [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 2, 01:41 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Lemur&oldid=51141271.


Karen Marais
BCB Hons NISL student
University of the Western Cape
Private Bag X17
Bellville

E-mail 2657211@uwc.ac.za

Web http://brit-journal.com/karen2006bcbnisl/

VARIATIONS IN SHELL STRUCTURE IN THE PHYLUM MOLLUSCA

The phylum mollusca contain animals that have shells ranging from “tiny snails, clams, and abalone to the octopus, cuttlefish and squid” 1. The mollusc’s mantle produces the shells made of calcium carbonate. 1, 6

To understand this better we look first at the anatomy of the molluscs. The posses a foot for locomotion, a shell, a mantle made of thin layers of body tissue covering the internal organs and an internal cavity covering the central part of the body from which most species have gills for extracting oxygen found in water. The shell is excreted by the upper surface of the mantle. The limpets (flattened, cone-shaped shelled marine molluscs) 2 produce the shell at the edge of the mantle at equal rates there by producing flat shells while other molluscs the front side secretes faster than the rear end producing a flat spiral6. Cowries are marine molluscs of the Genus Cypraea, and produce its shell by having maximum secretions along the mantle edges giving rise to a shell that look like a clenched fist. The shell is smooth and egg-shaped, with a long, narrow, “slit-like opening (aperture)” 3, 6. Some molluscs have one shell like the limpets or two (bivalves) like the mussels and oysters6.

Others like the chitons have shell plates. The dorsally carried calcareous armour shell of the chitons is protective and made of aragonite. They have diverse colours, patterned, smooth or sculptured. The shell is partitioned into eight articulating plates (valves) ‘embedded in the tough muscular girdle that surrounds the chiton's body’6. This formation helps chitons roll forming a ball when dislodged for protection and cling tightly to even irregular surfaces.4

The cuttlefish have their shells reduced and have formed an internal structure called the cuttlebone, which is porous to provide the cuttlefish with buoyancy. 6, 5 The octopus and the squid don’t have any shell but some species secrete a thin layer replica of the nautilus shell, the chambers of which are used to lays its eggs. The only hard part of the squid is the beak made of material known as chitin which it uses to get food6, 7.

In general all the molluscs that have shells use them for protection as they can roll into them and others go inside and hide into them. The chitons shell has colours that assist it in camouflage in the sea away from the predators. Others use the shell for buoyancy to help in the movements in water. Others like the squid have the shell modified to become a beak which they use to hunt their food with7.

Reference:

1. Wikipedia contributors. Mollusca [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 12:15 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Mollusca&oldid=51355000.

2. Wikipedia contributors. Limpet [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 4, 11:18 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Limpet&oldid=51510047.

3. Wikipedia contributors. Cowry [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 22, 10:53 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Cowry&oldid=49578379.

4. Wikipedia contributors. Chiton [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 1, 21:55 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Chiton&oldid=5

5. Wikipedia contributors. Cuttlefish [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 27, 13:49 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Cuttlefish&oldid=50421114.

6. Knight, R. BCB Biodiversity chapter 2 Building Bodies: Invertebrates Of The Oceans.
(Cited 2006 May 4) http://planet.uwc.ac.za/nisl/biodiversity/Chapter2/page_18.htm

7. Wikipedia contributors. Squid [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 4, 17:46 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Squid&oldid=53350566.



VINCENT MUCHAI WAIRIMU

Biodiversity and Conservation Biology

University of the Western Cape

Private Bag X17 Bellville

TEL: +27825103190

Email: 2648463@uwc.ac.za

Website:http://www.muchai.iblog.co.za

EVOLUTION AND INTERDEPENDENCE BETWEEN INSECT AND PLANTS

The earliest forms of plants that is the algae produced asexually and sexually (depends on water to transport the sex cells) 4. Moss represents the earliest forms of life to invade the land but encountered the same problem as the algae in terms of transportation of sex cells. The moss occupied the wet areas and didn’t have very specialised structures such as the roots4. As time progressed so as to be able exploit the land plants had to develop roots to be able to obtain water from the ground. Club mosses, horsetails and ferns were among the first vascular plants could stand on the ground before seeded plants appeared, some were tall plants up to 30m long.1,2,3,4 All of them had root to exploit and could be able to stand giving rise to the first forests. As forests were evolving also were the animals evolving to be able to occupy the habitats which include the insects group that had developed three segments of body head, thorax and abdomen, breathed through the trachea, had 3 jointed pairs of legs on the thorax. Insects have closer evolutionary ties with the crustaceans than millipedes even though grouped closer to millipedes.4

Originally insects climbed on vegetation but later developed wings, this helps them increase the surface area and for thermoregulation4. With the development of wings the insects were therefore entering into another phase to assist in plant reproduction. So also the plants were also evolving to avoid being victims of herbivores and desiccation especially the ones growing on the ground. Tall plants didn’t have problem a problem with the spore distribution spores as they would be blown by the wind but the sexual part with the transportation of sex cells by water meant that the sexual forms would remain shorter and closer to the ground exposing them to desiccation and being eaten by herbivores4. Ferns, horsetails and club mosses experienced this problem as they produced sexually through a structure called thallus which has sex cells on the lower surface where there is moisture all the time. After the female cell is fertilised it grows into a huge spore bearing plants4.

350 millions ago cycads evolved a different kind of reproduction by spores growing larger while still being attached onto the parent. They develop into conical-shaped structure with eggs. These spores called pollen are blown by wind and land on the egg bearing cones have a pollen tube which has secreted some fluid which aids it to swim to the eggs and fertilisation occurs. As this was happening various insects were evolving with modifications on wings formation. This was an advantage the plants were to make use for the transport of male reproductive cells (pollen) which are required to reach the female cells for fertilisation to occur and so new plants to develop. Wind dispersal of pollen was utilised by some plants like conifers but requires production of a lot of pollen4.

When insect were looking for food they could transport the pollen effectively; this was the point the plants exploited to have their pollen distributed. By alluring the insect with food the plants could have their pollen carried and this would mean less pollen production as compared to wind dispersal. This happened 100 million years ago with magnolias evolving flowers. Egg cells are clustered in the centre, each protected by a green coat with a receptive spike on the top called a stigma with which it receives pollen and is necessary for fertilization. Grouped around the egg cells with their stigmas are stamens which produce the pollen. This means the male and the female parts of the flowers are together but this posses the problem of cross pollination. This was solved by the egg and pollen cells maturing at different times. In order to attract the insects the structure is surrounded by brightly coloured petals and we have a complete flower. Beetles had learnt to feed on cycad’s pollen and were the first to venture to other plants like the magnolias and water lilies. They moved from one flower to the other collecting pollen meals but ended being covered by excess pollen which they delivered to the next flower visited4.

Different specialised methods of attracting insects for fertilisation purposes have evolved they include production of scented chemicals. Stepelia plants solicited flies for this purpose by evolution of flowers that mimicked the scent of rotting flesh and also had skin that looked like that of dead animal and generates heat to mimic warmth produced by decomposing flesh. Flies transport pollen and also lay eggs on these flowers. Others like the orchids evolved the sexual impersonation characteristic with one species having flowers that look like the female wasp even the eyes, antenna and wings and produce sex hormones produced by the female wasp. As the male “copulates” the flower, is covered by pollen and moves to the next flower to deposit pollen. 4

Other like the Yucca plant and the moth have a symbiotic relationship the flowering having pollen transported and the moth provide with food for caterpillar and a place to lay eggs4.

Reference:

1. Wikipedia contributors. Horsetail [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 4, 08:51 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Horsetail&oldid=51499558.

2. Wikipedia contributors. Lycopodium [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 30, 17:41 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Lycopodium&oldid=50913472.

3. Wikipedia contributors. Fern [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 2, 09:08 UTC [cited 2006 May 4]. Available from: http://en.wikipedia.org/w/index.php?title=Fern&oldid=51183313.

4. Knight, R. BCB Biodiversity chapter 2 The first Forests (Cited 2006 May 4) http://planet.uwc.ac.za/nisl/biodiversity/Chapter2/page_40.htm

VINCENT MUCHAI WAIRIMU

Biodiversity and Conservation Biology

University of the Western Cape

Private Bag X17 Bellville

TEL: +27825103190

Email: 2648463@uwc.ac.za

Website:http://www.muchai.iblog.co.za