Brief notes 4

Pollination by deceit

Mimicry, e.g. the hammer orchid mimics a female wasp. Some European orchids mimic female bees.
Deception, Rafflesia sp. and other similar species smell like rotting meat so deceiving flies into thinking the plant is a food source for their larvae.
Prey mimics, Epipactis consimilis (orchid) has little bumps resembling aphids. Hoverfly larvae eat aphids, so the female hoverfly lays her eggs on the labellum and pollinates the flower.
Aggressive mimicry, some arums lure flies deep into the flower with the odour of decay. The flies are then trapped for some time during which the flower is pollinated, then the flies are released.

Stephen Jay Gould on Natural Selection.

Stephen Jay Gould said that Darwin based the theory of Natural Selection on "two undeniable facts and an inescapable conclusion" - here they are:-
Fact 1. Individuals in a population vary in many heritable traits.
Fact 2. Every species or population has the potential to produce far more offspring than its environment can support with resources (food, space, etc.). This overproduction leads to an inevitable struggle for existence among individuals in the population/species.
Conclusion. Individuals with heritable traits best suited to the current local environmental conditions generally leave a disproportionately large number of offspring. This increases the representation of these heritable traits in the next generation. Darwin called this natural selection, and saw this as the cause of evolution.

Interactions between species and the effects.

+ = beneficial effects, - = harmful effects, 0 = neutral effects

Interaction
Effect on species A
Effect on Species B
Mutualism
+
+
Commensalism
+
0
Antagonism
+
-
Competition
-
-

Problems in designing new approaches to insect control

There are three main problems to overcome and no insecticide has overcome all three yet.
1) Avoidance of insect resistance.
2) Specificity. In some cases it would be preferable if the insecticides were species specific.
3) Persistence
It is unlikely that a neurotoxic pesticide will ever be formulated to overcome all three problems for any length of time as resistance will always occur.
1) Avoidance of resistance. This can be done by not putting the insect under selection pressure to develop resistance, e.g. using a variety of insecticides in an integrated pest management programme where insecticide use is only one part of the programme.
2) Specificity to the degree of species is difficult and perhaps only pheromones and parasitoids will be species specific. Bacteria, e.g. Bacillus thuringiensis can be specific the the level of family, but even here resistance had arisen through incredibly bad pest control. A watercress crop was grown year-round in glasshouses for 3 -4 years. During this time 40-50 applications of Bt strain for Lepidoptera was sprayed - surprise, surprise the target moth began to show resistance!
3) Persistence can usually be induced by chemical means, but persistence is the reason DDT was banned. So persistence must be modified so that the insecticide is just persistent enough to harm the target and not be present in the food chain. Antifeedant, parasitic nematodes, chitin inhibitors, and polyhedrose viruses can be persistent as they harm only the target.
Another problem is the investment of time and money a company must make before its product can be sold on the open market and make a profit before resistance is found. It costs tens of millions of pounds to get one successful insecticide through the trials, then the advertising and marketing before it starts to make a profit.

Adaptive value of animal colours.

1) Concealment from predators.
2) Advertisement; to frighten or startle potential predators, e.g. the eyespots of the peacock butterfly; to maintain territory or social rank, e.g. male peacock feathers; to announce sexual receptivity e.g. baboon rump patches.
3) Disguise as something unpalatable, e.g. the caterpillar of the comma resembles a bird dropping; or as something inanimate, e.g. stick insects.

Stages in animal cell division.

Interphase. 2 pairs of centrioles form by replication from a single pair. Around these form microtubules. Chromosomes duplicate, but cannot be distinguished individually as they are still in the form of loosley-packed chromatin fibres.
Prophase. Nucleoli disappear. Chromatin fibres fold and coil until individual chromosomes become visible. Each chromosome has duplicated chromatids joined at the centromere. Mitotic spindle forms between 2 pairs of centrioles. Later the nuclear envelope fragments.
Metaphase. Centriole pairs are at opposite poles. Centromeres of all chromosomes are aligned with long axes at right angles to spindle axis.
Anaphase. Paired centromeres move apart separating sister chromatids. Kinetochore fibres shorten pulling chromosomes to either pole. Poles move further apart each having a complete collection of chromosomes.
Telophase. Polar fibres elongate. Nuclear envelopes form. Chromatin in each chromosome starts to uncoil. 2 nuclei.
Cytokinesis. Cytoplasm divides. Cleavage furrow pinches and divides cell into 2.

Sense receptors

1. Chemoreception. This is the most primitive and universal sense in the animal kingdom. It can be split into two types; contact chemoreceptors which orient an animal away from or towards the source, and distance chemical receptors including the sense of smell and pheromones.
2. Mechanoreception.
This includes touch, vibration and motion. These receptors allow the animal to move, feel and interact with its surroundings.
Photoreceptors.
This is vision. These receptors can be simple, light-sensitive cells on the body surface of the animal, or more organised eyes such as the compound eyes of insects and cephalopods.

Keystone species

A species whose disappearance from a community transforms the populations of the other species in the community. For example the sea urchin Diadema antillarum's die off in the Caribbean led to a huge increase in the algal community, and a decrease in productivity and diversity of the coral reef. The removal of the starfish Pisaster ochracecus from a Pacific coastal community led to a population explosion of the mussel Mytilus californicus and the disappearance of nearly all other animals and algae.