D.2c: Species and Speciation: Sympatric Speciation

03/09/2013 § 1 Comment

It is with deep and utter sadness that I report to this blog that some animals and plants are unable to reproduce. What a sad, sad day it is.

Okay, in all seriousness, there is a reason why most plants and some less complex animals can’t make babies (therefore they are sterile or infertile). This occurs with polyploid organisms, which means that they have more than two sets of homologous chromosomes as a result of hybridisation between two different species. This is all centred on the number of homologous chromosomes an organism has and whether or not it’s viable for meiosis during reproduction. A tetraploid, for example, has an even number of homologous chromosomes and the gametes would then be diploid. If tetraploids mate with tetraploids, then the number of sets for the kid would still be okay. If a tetraploid (gametes are diploid) mates with a diploid (gametes are haploid), then the offspring would be at a disadvantage because it would be triploid. It wouldn’t be successful in meiosis therefore wouldn’t be able to reproduce any of its own offspring essentially rendering it reproductively isolated from the rest of the original population. Too bad, son.


Lacewing songs, page 313

1. Compare the songs of the two species of lacewings.

The first lacewing’s song is more constant than the second lacewing’s song. The pattern is the same throughout the 30 (units of time). The second lacewing’s song starts off quiet, gradually builds in a crescendo (crescendo!) and remains roughly in between 3 and -3 dB. Both lacewings’ songs range between 4 dB and -4 dB. The second lacewing gets quieter at 10 (units of time) and (probably) quiets down afterwards but the first lacewing just keeps going.

2. Explain why differences in mating songs might lead to speciation.

A different mating song indicates different behavioural isolation that is part of reproductive isolation. The two different mating songs means that lacewing species A is going to attract different potential mates that will respond to their call than those which species B will attract. This could also mean that species A would mate at a different season than species B. Ultimately, because of the differences in mating songs, the lacewings would attract different mates under different conditions and reproduce different offspring. Following that, the two new kinds of lacewing would be different from each other and would continue to evolve separately if the difference mating songs continue to be used.

3. The ranges of the two species currently overlap. Suggest how differences in song could have developed:

  • a) by allopatric speciation: If it were allopatric speciation, a geographic component of their habitat needed to have changed in order to separate species A from species B. Any geographical changes meant the lacewing would have to evolve and change their song in order to keep making babies. Maybe their forest was cut down and some of them had to move to another forest because SURVIVAL. Humans, am I right?
  • b) by sympatric speciation: It it were sympatric speciation, that means all lacewings are still in the same geographical area. One possibility would then be genetic pool isolation, for example the ploidy of some of the lacewing organisms could have been insufficient for reproduction so hybrid zygotes would fail to develop or reach maturity and create a different species out of them. …Maybe.

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§ One Response to D.2c: Species and Speciation: Sympatric Speciation

  • Dave Ferguson says:

    Blog DP

    Grade 7 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them almost faultlessly in a wide variety of situations. Consistent evidence of analysis, synthesis and evaluation is shown where appropriate. The student consistently demonstrates originality and insight and always produces work of high quality.

    Data-based questions page 313
    • Duration of song: a > b
    • Duration of notes: a > b
    • Variation in frequency: b > a
    • Number of notes: b > a
    • Maximum frequency: a = b

    • biological species concept: species = group of organisms
    – capable of interbreeding and producing fertile offspring
    – isolated from other group
    • mating calls
    – act as reproductive isolating mechanisms
    – are pre-zygotic
    – are species speccific

    • geographical isolation
    • divergence due to unique selective pressures
    • reproductive isolation

    • ecological isolation
    • divergence due to unique selective pressures
    • reproductive isolation

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