The exciting life history of Ulva spp.

Today’s edition of our introduction to the world of algae took us down the convoluted path of algae life histories and reproduction. It’s not as simple as the birds and the bees may suggest..

Algae posses three different, distinct life history strategies;

  1. Gametic meiosis; The free living organism is diploid (like our normal  body cells). In this case gametes are produced via meiotic division. eg. Fucus spp. and Codium spp.
  2. Zygotic meiosis; The free living organism is haploid (like our eggs and sperm). Now gametes can be produced merely by mitotic division. eg, Chlamydamonas, a green microalgae. This method of alternation of generations is not as common in the macroalgae.
  3. Sporic meiosis; Now the free living organism possess diploid and haploid regions.This enables gametes (N, haploid) and spores (2N, diploid) to both be easily produced. eg. Ulva spp.

So! Sporic organisms like Ulva spp. have the ability to have one lobe of their tissue producing gametes, whilst simulaneously the neighbouring lobe is releasing spores. But how could you tell what kind of cells Ulva is releasing? 

Despite the similar appearance and release locations of diploid and haploid cells by Ulva the different purposes of these cells reveal their identity. By shining a light towards newly released gametes/ spores will result in a distinct gravitation towards the light for gametes (hoping to disperse and find another) or movement away from the light for spores (hoping to fund substrate to settle upon). 

This simply tested phototactic response by the cells clearly indicates whether that certain lobe of the Ulva is then diploid or haploid in nature.

We were lucky enough to observe this phenomenon directly after learning about the process in Ulva

Image

Gametes released by Ulva spp. exhibiting a positive phototaxic response to light.

Here we can see the thousands of microscopic green gametes that have just been released by the Ulva into the water. Their positive phototaxic response to the light indicates that this section of the organism is halpoid in ploidy and producing gametes.

There you have it! The first step to understanding the complex world of algal reproduction thanks to our abundant friend Ulva spp.

 

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