Variations on a theme, Part IV

The most common invasive plant in the Maltese countryside is the Cape Sorrel (Oxalis pes-caprae L.). The pictures below, taken at Għajn Tuffieħa, show the usual variety of the flower (1), together with another less frequent form exhibiting extra petals (2) resulting from additional sets of chromosomes in the cells' nucleus (polyploidy).

It is known for its sour taste resulting from a reserve of oxalic acid in the plant tissues, which has also resulted in its Maltese vernacular name of Qarsu (=sour).

(1)

(2)

Variations on a theme, Part III

Chrysanthemum coronarium, known locally as 'Lellux', is an extremely common plant preferring to grow in 'disturbed' habitats like fields and degraded garigue. Around this time of the year it colours whole landscapes as carpets of flowers are produced to compete for pollinating insects, one of which is the beetle Oxythyrea funesta (Poda, 1761), shown below.

As can be seen in the above photograph, the colour of the flower is a bright yellow bordering on orange. This is generally common for most individuals; such a noticeable array of petals contributes to frequent pollination and therefore the yellow flowers are selected for, passing on their genes. Despite this, as in all other organisms, genetic variations that contribute to a different flower appearance do pop up from time to time. The most common of these variations is a dichroic scheme to the petals, with a discoloured (white) area appearing over part of the flower's diameter, the extent of which varies from one affected flower to another.

Most of the time, these aberrations consist of solid bands of colours, though a few may show small yellow flecks scattered over the white area.

Very rarely, the white and the bright yellow colours are not separated from each other, but mixed evenly throughout the flower, resulting in a pale yellowish flower that is far less conspicuous than usual ones.

Variations on a theme, Part II

I have finally decided to change the appearance of the blog title by including some pictures of its namesake, which in actuality deserves a post all to itself.

The genus Muticaria Lindholm, 1925 from the peculiar family of landsnails knows as the Clausiliidae (door snails), is endemic to Sicily and Malta. Only one species exists on Malta, consisting of four main forms variously regarded in contemporary literature as varieties (Giusti et al., 1995) or actual subspecies (Nordsieck, 2007). Likewise, two main forms exist on Sicily, also regarded either as varieties of the same (Giusti et al., 1995) or as altogether different species (Beckmann, 1990).

The entity endemic to the Maltese Islands, namely Muticaria macrostoma (Cantraine, 1835) has, since the Pleistocene, diverged into local and very characteristic (though hybridizing) varieties, two of which are extremely limited in distribution. The typical forms are shown below.

I would like to thank Mr. He Jing for the excellent photographs and also for the permission to use them.

Muticaria macrostoma macrostoma (Cantraine, 1835) - Ħ'Attard

Muticaria macrostoma mamotica (Gulia, 1861) - Munxar

Muticaria macrostoma oscitans (Charpentier, 1852) - Dingli

Muticaria macrostoma scalaris (Pfeiffer, 1848) - Mistra

References:

Beckmann, K.-H., 1990. Beiträge zur Kenntnis der Landmolluskenfauna Siziliens mit der Beschreibung von Muticaria neuteboomi spec. nov. (Gastropoda: Pulmonata: Clausiliidae). Basteria, 54 (1/3): 75-85.
Giusti F., Manganelli G. & Schembri P.J., 1995. The non-marine molluscs of the Maltese Islands. Monografie Museo Regionale di Scienze Naturali, Torino, 15: 1-608.
Nordsieck, H., 2007. Worldwide door snails (Clausiliidae), recent and fossil. Hackenheim: Conchbooks, 214 pp.
Schembri, P.J. & Sultana, J. (eds.), 1989. Red Data Book for the Maltese Islands. Malta: Department of Information, pp. i-viii + 1-142 + 8 pl.

Variations on a theme, Part I

The sea snail Columbella rustica (Linné, 1758) is a very common inhabitant of Maltese rock pools and shallow platforms. It has a large range, extending from the Mediterranean down to the coasts of Angola and the eastern Atlantic islands.

The shell is highly variable, even within relatively short distances in this range, since it relies directly on the habitat. Specimens from the northwest of Malta tend to be mostly small and dark, while others from the sandy beaches of eastern Malta are light coloured and much larger (photograph below). This can be explained by natural selection - yellow specimens are better camouflaged against the sand, while mechanical damage to the shells by waves is not a pressing problem in a soft substrate such as sand. The small compact individuals from rocky shores, on the other hand, are exposed to very rough currents, which may dislodge and batter the shells onto rocks, therefore a smaller surface area works better in this regard. The darker colour also conceals shells in the algae better than light ones.

In addition to population-scale differences, there is also some variability on the individual level. The above photograph, on the extreme left, shows a 'freak' elongated specimen with convex whorls. A 'turriculated' variety from the same area is figured below (photo by Constantine Mifsud).