Based on what I've read it is believed that the so called German Ostsiedlung in Wielkopolska took place only on a small scale.
For example a 1958 book "Historia Polski" ("History of Poland") Volume I, Part I, page 370, says:
"(...) colonization with use of German settlers was limited just to some provinces such as Silesia, Western Pomerania and Prussia, while in Lesser Poland and Greater Poland [Wielkopolska] it occured only on a small scale, and was nearly unknown in Masovia."
However, when comparing autosomal DNA of the inhabitants of Wielkopolska from the Early Piast period (an average of 36 individuals - from Ostrow Lednicki, Lad, Rumin, Dziekanowice, Legowo, Oblaczkowo and Poznan - their average dating is ca. year 1100 AD) with modern inhabitants of Wielkopolska (an average of 9 individuals, but the territorial scope is from nearly entire Wielkopolska - 4 people from northern Wielkopolska, 3 from southern, one from western and one from central) it turns out that Early Medieval Wielkopolans resembled modern Belarusians, while modern Wielkopolans are much more shifted westward, towards Germans.
In this PCA I compared a dozen Belarusians, a few dozen Germans and averages for Early Medieval and Modern Wielkopolska:
https://i.postimg.cc/T2Mg6pLQ/Wielkopolska-PCA.png
^^^
This indicates that throughout the centuries Poles from Wielkopolska absorbed and Polonized a large number of "Westerners".
A simple Vahaduo test modelling Wielkopolska Poles as a mix of Dutch and Early Medieval Wielkopolska, gives such results:
(I used Dutch because the German average has Slavic admixture, and I assume that Ostsiedlung settlers didn't yet have it)
Target: Wielkopolska_Modern(n=9)
Distance: 1.3772% / 0.01377226
71.4 Wielkopolska_Medieval(n=36)
28.6 Dutch
We can also test this model with an average of Poles from Bydgoszcz in Kuyavia (which is sometimes considered a subregion of Wielkopolska). This average is composed of hospital patients from Bydgoszcz, so we don't really know their genealogy, and some of them might hail from other regions of Poland:
(Here I also used the Wielkopolska_Medieval average because the number of Early Medieval samples from Kuyavia is very low)
Target: Polish_Bydgoszcz(n=70)
Distance: 0.9185% / 0.00918509
77.4 Wielkopolska_Medieval(n=36)
22.6 Dutch
Let's add that the percent of surnames of Germanic origin among ethnic Poles from Wielkopolska today, is around 10%.
So it seems that the majoirty of this Western admixture had to occur in times before surnames became commonly used.
Coordinates used:
What do you think about this?Code:Wielkopolska_Medieval(n=36),0.1289046,0.1255025,0.0766078,0.0709792,0.0410247,0.0252861,0.0067696,0.0129931,-0.0002898,-0.025999,-0.0019983,-0.009579,0.0186445,0.0224095,-0.0092893,0.0023976,0.0061498,-0.0001653,0.0028421,0.0016779,-0.0030051,-0.0057155,0.0079871,-0.0061453,0.0009846
Polish_Bydgoszcz(n=70),0.1331242,0.1298572,0.0726065,0.0610516,0.0418407,0.0241559,0.0088296,0.0115215,-0.0008035,-0.0183694,-0.0028348,-0.0062815,0.0113109,0.0184945,-0.0058825,0.0008807,0.0016522,-0.000029,0.0020399,0.0015525,-0.0029644,-0.0027752,0.0055444,-0.0022085,-0.0001574
Wielkopolska_Modern(n=9),0.1327936,0.1347269,0.0687617,0.0590013,0.0383318,0.0226831,0.0086168,0.0080254,0.0000683,-0.0191551,-0.0038251,-0.0063443,0.0124214,0.0151079,-0.0067257,0.0026664,0.0025498,0.0005912,0.0011312,0.0020286,-0.0042563,-0.0022257,0.006354,0.0035479,-0.0016364
Dutch,0.127441,0.134179,0.060271,0.044076,0.040844,0.016397,0.005402,0.007263,0.004209,0.001924,-0.005635,0.004427,-0.009846,-0.008676,0.01783,0.005623,-0.006516,0.001748,0.003909,0.002816,0.00448,0.003385,-5e-06,0.013892,-0.000656
