Winter Highlights and the harbingers of Spring 2013

I spent most of the winter in Johannesburg and this year’s weather turned out to be very mild. I spent a lot of time hiking in the Klipriviersberg, occasionally getting out and seeing other places around Johannesburg. Winter in Johannesburg is dry with warm days and cold nights. The sky is blue and the landscape becomes predominately fawn with darker and lighter colours standing out here and there.

A grassland scene from Suikerbosrand just south of Johannesburg.

Due to the generalised diminished activity of life forms in winter, everyday aspects of life begin to attract attention. A plant flowering or a minute crawling arachnid become points of interest that would not be as engaging had they been observed in the bounty offered by summer.

A 'large' free-living predatory mite of the Trombidiidae family. Mites are considered the most diverse group of animals after insects. Over 40 000 species have been described and 2 350 have been recorded in South Africa. 

This Aloe greatheadii var. davyana flowered early in winter. Standing out on the dried out landscape.

Later in the season large areas of the hills were covered in flowering aloes. 

The reason for this floral display: pollination, using insects in the the swapping of genetic material between individual organisms.

When walking in a dry landscape sources of water become a space where life congregates. This slowly moving river in the Suikerbosrand, along the Bokmakierie trail is full of algael life and water plants. The absence of life around the stream draws ones attention to what is happening in the water.

A slow moving stream with algae and water plants, an ecosystem.

Looking closer at the algae in the stream one notices many bubbles that have formed amongst the string like structures of the algae. What is happening is that the algae are photosynthesising. They are turning sunlight into energy and this process of photosynthesis is so important: all the food we eat and all the energy we use (fossil fuels, fire wood etc.) are products of photosynthesis.[1]

Oxygen being released as a waste product from algae.

Looking at a scene like this one can recall the early days of life on earth. Algae and other photosynthesising organisms that inhabited aquatic environments slowly, through bubbling oxygen as waste product, started to create an excess of free oxygen, first in the aquatic environments and then later the atmosphere. The process must have taken millions of years, but in time there was enough oxygen for new oxygen dependent organisms to develop. In time the atmosphere was filled with enough oxygen to allow animal life dependent on oxygen to begin colonising the terrestrial habitats. 


During a cold winters day I took a drive out to a wet land area to the east of Johannesburg called Marievale Nature Reserve. The reserve is in the middle of a rich gold mining area. There are mine dumps on the reserve and the water is no doubt being poisoned slowly through acid mine drainage. Yet there is a lot of life in the reserve. I saw many water birds and even a pair of Large Grey Mongooses (Herpestes ichneumon) which according to the reference material falls outside of their distribution.

A pair of African Fish Eagles (Haliaeetus vocifer) with a mine dump in the background.

Closer view of the African Fish Eagles.

The reserve has many interesting water birds. In the few hours I was there I saw some very interesting species: African Snipe, Cape Shoveler, Red-billed and Hottentot Teals as well as masses of Red-Knobbed Coots and many Little Grebes (Dabchick).

Red-knobbed Coot (Fulica cristata), these birds are very aggressive and dominate most other birds in their home range.

Little Grebe (Tachybabtus ruficollis), a tiny waterbird. Grebes are unique among birds in the habit of swallowing their feathers to prevent injury while regurgitating fish bones and other indigestible material.

In the dry winter landscape, fires often move through large areas, leaving a strange black landscape. In these burnt out areas life continues as the fires are considered cool and they move fast. The damage is often superficial and an important part of the rejuvenation of grassland. In these black patches, even the drabbest birds stand out.

Cape Longclaw (Macronyx capensis) moving through burnt grass looking for insects.

Unlike most mammals the Rock Hyrax or Dassie (Procavia capensis) have little control of their body temperatures and sunbathe and also huddle together at night to keep warm. Hyraxes superficially resemble rodents, but they are from a different order that includes elephants, dugongs and aardvarks. The Hyravoidea family was once one of the dominant herbivores on earth and there were some that grew as large as pigs. With the rise of ungulates the order was unable to compete and now only the smaller forms remain.[2] 

Rock Dassie sunning itself.

In order to take advantage of the rains that may come in spring, many plants begin to flower in winter. This will allow them to drop seed during the early part of the rainy season and ensure that their offspring gets the maximum advantage of a warm wet summer.

Aloe marlothii in flower. Many birds are attracted to the flowers and help pollinate this plant. In the background the suburb of Glenvista is visible. I live in there somewhere.

Ledebouria ovatifolia floweing. These small plants grow close to the ground and flower late in the dry season.

These Moraea stricta flowers are also late winter bloomers.

In anticipation of spring, the Common Wild Pear (Dombeya rotundifolia) produces blossoms.

The Camphor Bush (Tarchonanthus camphoratus) has already flowered and set seed.

This Shield-back Bug (Scutelleridae) nymph has capitalised on the food source provided by the Camphor Bush. It is feeding on the seeds.

On days when there is not much to see, marks in the sand stand out and indicate rich interactions that have taken place unseen.

This porcupine track and dung point to a species that is very rare to see, yet it is a common animal. Porcupines are very secretive and strictly nocturnal.

Lichen slowly grows on rocks. Lichen is a composite organism that is made up of a fungus and an algae. The algae photosynthesises and creates a food source for the algae; the fungus provides moisture and a structure on which the algae can live.

A striking yellow lichen growing on a basalt rock.

Close-up of the lichen, its structure and growth form can be seen. Some lichens slowly chemically erode the substrate they are growing on.

This grey lichen has a more pronounced foliose structure than the yellow form.

Below are some interesting things I saw while walking in different places.

This gum that is being exuded from a Sweet Thorn Tree (Vachellia karroo) is edible and was once marketed as 'Cape Gum'.

This pair of Hadeda Ibises (Bostrychia hagedash) have become such a common sight in suburban Johannesburg, that they seem a little out of place here in their natural habitat. Photographed in the Klipriviersberg Nature Reserve.

Thickbill Weaver (Amblyospiza albifrons subsp. woltersi) perching in reeds at James and Ethel Gray Park in Melrose, Johannesburg. These birds have found a sanctuary in the vegetation around a small dam in the middle of suburbia. Practically, right next to the M1 Highway, one of the busiest roads in South Africa.

Winter is a time of death. Many organisms that are not strong enough succumb to the cold and die. Vegetation dries out and dies back, often fires sweep through areas and burns moribund and kills the weak. This process is important in strengthening populations of organisms.

Even though this process of death is happening all over, life is still strong and the more robust organisms continue to live (at a slower pace) and one does not need to look hard to find life just waiting to for the warmth and rains to return. With the return of warmth come the harbingers of spring. Animals that have been waiting in dormancy for the return of life.

A bat of the Vespertilionidae family foraging in the early evening. Picture taken at the Klipriviersberg Nature Reserve. Bats hibernate for the winter months. Emerging again with the warmth and return of their insect prey.

Summer is returning when reptiles start to emerge from their brumation. Below are the first reptiles of the season.

Cape Centipede Eater (Aparallactus capensis). A specialised feeder which feeds on centipedes which it overpowers with its venom. The snake is completely harmless to humans.

Southern Rock Agama (Agama atra) basks in the sun on it's rock. This lizard will spend the summer defending this rock from up and coming males and mating.

Transvaal Gecko (Pachydactylus affinis). This geckos tail was thin, showing that it used up its fat reserves during the winter. By the end of summer its tail will be good and fat.

[1] For a more detailed discussion of photosynthesis see Van As, J., du Preez, J., Brown, L. and N. Smit. 2012. The Story of Life & The Environment. Struik: Cape Town (131-138).
[2] See Estes, R. D. 1993. The Safari Companion. A Guide to Watching African Mammals. Russel Frieman Books: Halfway House (214- 222).

Rust Fungus

Deformity on stem of Vachellia Karroo, caused by Sweet Thorn Rust (Ravenelia macowaniana).

Rust fungi belong to the order Pucciniales and are represented by 540 species (in 40 genera) in Southern Africa and around 7 000 species globally.[1] Despite their prevalence in the environment, rust fungi are generally overlooked in the natural environment. The relationship of rust fungus to the host plant is a pathogenic parasitic relationship. The fungus is an obligate biotroph, meaning that they cannot live outside of their host organisms. Rust fungi exhibit complicated life cycles and some develop five distinct types of spores at the different stages of their life cycles.

Vachellia karroo, normal plant structure. No galls present.

 One of the most widespread species in Southern Africa is Ravenelia macowaniana or Sweet Thorn Rust. This species has all the spore types present in its life cycle. It lives in the Vachellia karroo (Acacia karroo) plant making this species of rust fungus particularly widespread and common. The life cycle of the fungus is complicated.

Ravenelia macowaniana gall. Note the small holes on the gall, these were made by moth larva feeding on the gall.

Summarised from Alan R. Wood, the life cycle can be described as follows:

In the beginning of the growing season, the galls develop on new growth and on these galls “blister-like structures” (pycnia) manifest. These produce minute spores (pycniospores) in a sweet suspension that attracts insects which feed on the substance and spread the spores. This creates a situation of “cross fertilization” and results in “small cup-like aecia [that] are produced all over the galls” and in these asexual spores (aeciospores) are produced which go on to infect the leaflets of the plant. These leaflet infections then initially produce another asexual spore that appears like blisters (uredinia) on the surface of the plant. These uredinia go on to produce urediniospores. Towards the end of the growing season structures called the telia produce the large teliospores which “after overwintering, germinate in the next rain season to begin the cycle again. When germinating these teliospores produce four basidiospores, each of which can infect the new, developing growth producing the [pycnia] galls.”[2]

Ravenelia macowaniana gall. Aecial cups are visible here, indicative of the early parts of the fungus life cycle.

In addition to the fungi and tree relationship, there is a third relationship and that is between the galls and Lepidoptera species (gall moths). There are at least 24 species and they belong to the Tineidae, Oecophoridae, GraciIlariidae, Gelechiidae, Cosmopterigidae, Tortricidae, Pyralidae and Noctuidae families. [3] M. Krüger (1998) groups the moths into three guilds: “putative obligate species, i.e. those feeding on gall tissue … A second significant guild comprises polyphagous species that develop as borers, mostly in fruits and pods of their host plant … The third guild includes species that are probably predators of other larvae” (55–56).  The life history of these moths is, as Krüger himself puts it, “obscure”.  

The obligate species of moths associated with the Ravenelia macowaniana are an example coevolution. That makes the relationship between the tree, the fungus and the moths incredibly old. All three have been evolving together into their current coupling. The tree seems to be relatively defenseless against the rust. I have noticed that trees growing in less than perfect locations exhibit more of the disease. It would be interesting to find out more about the trees defenses against the rust.

Thinking about the intricacies in the relationship between this tree and the fungus that lives inside it and the relationship of the moths to the galls produced by the fungus in collaboration (even though it is through disease) with the tree, just demonstrates that we are surrounded by biodiversity of such a magnificent scale. Just looking at something as small as fungal structures on the surface of tree can reflect relationships and interactions that are not even well understood. In trying to find out what the cause of the structures are; moths and a strange world of fungus is called up. This is the mysterious world of nature that has makes my brain burn with wonder.

 

---

[1] For an overview of the taxonomy of the Pucciniales see: http://www.plantmanagementnetwork.org/proceedings/FCRS/2011/Presentations/Aime.pdf

[2] Adapted from Wood, A. R. (2012). Rust fungi on South African plants. Veld & Flora, 3 (98), 123– 125. 

[3] For a discussion of the moths see: Krüger, M. (1998). Identification of the adults of Lepidoptera inhabiting Ravenelia macowaniana Pazschke (Uredinales) galls on Acacia karroo Hayne (Fabaceae) in southern Africa. African Entomology 6, 55–74.